In the pilot of the Disney series, Doug remembers having fun with Mr. Bone the assistant principal and Skeeter informs him Mr. Bone was a dick. There was an episode of the original series where Mr. Bone lightens up after having surgery and acts like a kid again. He also befriends Doug and this could've been a flashback to that.
In the same flashback, Doug remembers Skeeter saying "Don't forget the Beets concert in homeroom." This is obviously supposed to be another Fake Memory, showing Doug remembering the past as rosier than it was. But fans of the original series will remember that the Beets did give a concert at the school in one episode. Doug is probably remembering that, just misremembering it as an everyday thing instead of a special one-time event, just like he misremembers Mr. Bone as having always been his friend.
How does Mr. Dink afford the latest and "Very Expensive" tools and gadgets? Early in the series he mentions that he's a writer, he's probably testing and writing product reviews for them.
It's also been stated that he and his wife have no kids and two incomes so naturally there's a lot of extra money lying around. This adds further Fridge Brilliance if you consider "DINK" is also an acronym for "Double Income, No Kids".
In "Doug's Fat Cat," Stinky demands to be fed pickle-flavoured ice cream. Strange for a cat—you'd think he'd want something like liver, or tuna flavour. The choice actually becomes subtle foreshadowing after a rewatch— in humans, both pickles and ice cream are stereotypical pregnancy cravings, and Stinky was very pregnant at the time!
The fact that Roger stated he was putting Stinky on a weight loss diet is also foreshadowing. Because Stinky's pregnant.
The flashback in "Doug rocks the House" may turn surreal when Patti shows up in it throwing a rock at it. But aside from being symbolic of Doug's empathy for what he did, it's also a Stealth Pun for a saying ("People in glass houses shouldn't throw stones"). He realized he was being a hypocrite by calling something Patti considered sentimental "Just a crummy old house", when he wouldn't appreciate someone destroying his childhood home.
In the episode "Doug Clobbers Patti" he tries to break a winning streak he's having against Patti Mayonnaise by breaking mirrors, running under ladders, and doing this weird ritual Skeeter's aunt has. Afterwards, he's tripping over thin air, his bike tire blows for no reason and a car splashes mud all over him. When he starts a bowling match against her, he's still winning, without even trying. Why? He wants to lose, and his bad luck is keeping it from happening!
Judy is normally a bit of an antagonist towards Doug, but has a lot of Pet the Dog moments (moreso than Roger). This makes sense if you do have a sibling, actually - Doug is an Unreliable Narrator so he'll up Judy's Jerkass-ishness a bit. Plus, Judy's just getting older - usually most siblings get better to their Annoying Younger Sibling when they get older and more mature (keyword being usually... tropers can name a few siblings they hate well into adulthood).
The pilot to the Nickelodeon series foreshadows the plot of Doug's First Movie, since it involves searching for a rare creature in the lake.
Patti is a good singer in the Nickelodeon show, but is Hollywood Tone-Deaf in the Disney version. It's possible this is due to her going through puberty.
The rich girl's Beebee Bluff's head, along with her ponytail, look like they're shaped like a money bag.
In "Doug Takes A Hike" Roger tries to scare Doug by telling him of a tree that was punching a former camper, and Doug believes him, followed by a fantasy of scary trees. While Doug can be gullible, we learn in future episode that in the Bluffington Founders play that the settlers were told by trees to go found their town somewhere else. Doug might've heard the story by this point, thus making the idea of living trees not so far fetched.
At the end of "Doug's Career Anxiety," Mr. Shalackey's new assessment that Doug's ideal career is guidance counseling isn't necessarily just a Here We Go Again!. Doug probably would make a good guidance counselor. Even at eleven, he's very kind and empathetic for his age, is good at understanding others (e.g. when he figures out why Roger sabotaged the wheelbarrow race in "Doug and Patti P.I."), connects well with younger kids (e.g. in "Doug's Fan Club"), and he's a good communicator when his anxiety doesn't get the best of him. As an adult he would remember his own preteen anxieties and social awkwardness and would relate well to the same problems in kids. He could be a much better guidance counselor than the obnoxious and creepy Mr. Shalackey ever was.
Word of God saying that ten years into the future Doug and Patti aren't together despite the ending of the Disney version actually fits well with what see across the original series and even the Disney one to a point. It's repeatedly shown that Doug doesn't really "know" Patti, going from his many fantasies where he either treats her like a "pure" damsel/princess who fawns over him for solving whatever problem's happening, or else a harpy who turns on him whenever he displeases her, rather than just seeing her as a girl with her own hopes, dreams, fears. We're shown in episodes like "Doug Clobbers Patti" (where Doug repeatedly beats Patti at games and she's a bit of a sore loser) or Disney's "Doug's Minor Problem" (the episode with G-Rated Drug Nic-Nacs, which has Patti take one at a party) that Patti isn't as perfect as Doug thinks she is. Nor is she ever as judgmental as Doug worries she'll be. Is it any surprise they don't get together (or in the Disney version's case, don't stay together)?
In "Doug Loses Dale," Judy's initial advice to Doug about babysitting, "To fully understand a child, you have to become a child," is actually the most sound advice he gets. Doug ignores it because Judy phrases it in her usual melodramatic way, but in the end it's precisely by putting himself in Dale's shoes and remembering what he used to do when he was a toddler that he figures out where Dale is hiding. Judy might be a Cloud Cuckoo Lander, but in this case she knows what she's talking about.
The flashback sequence in "Doug's Christmas Story" shows Porkchop being given to Doug for Christmas when Doug was about five years old. (Although "Doug's Dog's Date" contradicts this with a flashback of Doug riding on Porkchop's back as a baby, we can chalk that up to Early-Installment Weirdness.) In the Disney episode "Patti's Dad Dilemma," we learn that Doug had a hamster named Happy that died when Doug was five. Phil and Theda must have wanted to cheer Doug up after Happy died, so that Christmas they got him a dog.
In the cooking episode, it's established there is an odd number of students in Mrs. Wingo's class. This is why Doug was paired with both the Sleeches during the "Weird kids" episode - Wingo counts them as one for the purpose of that assignment.
Why Patti goes to the middle school for Science and Sports makes sense when you consider that an actual school building is more likely to have access to more advanced equipment than home school - and they have sports teams. In real life, homeschooled children sometimes do this for sports.
Why do the rest of Doug's relatives have different skin tones than him? Judy's tan, his dad's orange, his mom's pink, and his Grandma is yellow? He wasn't adopted and the rest of his friends have the same skin tones as their parents.
This could be chalked up to Doug's Unreliable Narrator status, given how everyone else is a different color scheme due to being a cast of colorful characters compared to the (admittedly dull) focus protagonist who has a realistic skin tone. Not to mention how the colors could very well reflect how he perceives his family members. A bit of a stretch, but it could account for his Mother being pink (being the sweet but sometimes embarrassing maternal figure) and Judy being tan (older age and perhaps also her stage lighting-tanned melodramatic actress persona).
Judy was also shown to practice martial arts, suggesting she might be notably more physically active (hence the tanned skin).
If Beebee Bluff's family is so rich, why does she go to a public school?
Because her family is the only one rich enough to pay for private school and Bluffington doesn't have one. Or she just wants to go to public school.
Actually, this could be Fridge Brilliance - sending rich kids to public school may actually be a way to Break the Haughty. (Along with being able to save money.) A lot of private school graduates who grew up from rich families are... a little unaware of reality, and they never even mildly understand what people in different economic backgrounds go through.
If Doug based all his Quailman villains on people who antagonized him in real life... then what the hell is "Dark Quail" based on?
In the episode "Doug's Career Anxiety" Doug is going the task of being in charge of a school assignment with Connie, Beebee, Chalky, and Skeeter. When things get hard to handle he runs off and has a fantasy where he's been running away everyday of his life. Connie is nowhere to be seen in his fantasy. Did Doug imagine that Connie died? Does Doug want that to happen to her?
Doug has some seriousmental problems, and NO ONE seems to care. He has repeated and vivid hallucinations that he physically acts out in front of his friends and family, and they just laugh it off, even though it's almost gotten him killed a few times (like the times he blanked out IN THE MIDDLE OF A BUSY STREET, or while driving soapbox racer down a hill). What the hell is wrong with these people?!?! They need to get him treatment before he fatally injures himself or someone else!
In the episode "Doug's Older Woman" from the Disney series, there was the girlfriend dujour that pointed out how funny Doug was acting multiple times, with him denying it (since he doesn't remember the fantasies he was acting out). Now since she only appeared in that episode she probably didn't witness some of his worst fantasies (like the fantasy he has while in the middle of traffic), but the fact that she is named Cassandra does add some Fridge Brilliance on top of the Fridge Horror.
Unreliable Narrator mean anything to you? We're probably just seeing things colored by Doug's point of view. When he's gotten hurt as part of the actual plot, his friends react appropriately.
In "Doug Tips The Scales" his Grandma Funnie spoils him with excessive junk food which causes him to gain weight. His grandfather is nowhere to be seen, which means it's possible he died from diabetes or a heart attack due to his wife's coddling.
When Patti develops an eating disorder, running herself into the ground and eating spray food from aerosol cans when she eats anything at all, Doug naturally gets worried and goes to the coach...who says Patti is doing the right thing. Let me repeat that; he is so inattentive that he believes a girl starving herself and over-exercising is good self-care. Even after she faints during a race, he expects her to just get back up and go back to running, until thankfully Miss Kristal tells him off.
None of the kids in "Doug Is the Hamburger Boy" were wearing lifejackets, not even Al or Moo. Had it not been for Doug, they all could have easily drowned.
If you consider the Disney series part of canon, the fact that they're swimming in Lucky Duck Lake, where Bluffco dumps toxic waste & industrial runoff into which by the way created the Lucky Duck Monster, is even more horrifying. Likewise when Doug and Mr. Dink get soaked in the same lake when their fishing boat sinks in "Doug's Big Catch."
In the episode "Doug's Fat Cat", Stinky the cat actually was in danger of dying, just not for the reason Doug thought, as he didn’t know at the time. Pregnant cats usually slip away to a dark, quiet place when the time comes and give birth with no trouble and a minimum of noise. When you remember the way Stinky was howling and carrying on, it becomes clear that her labor was almost certainly obstructed. Hammered home when Doug overhears the vet, who appears to be performing a surgical procedure with the help of a tech, say "If they'd brought the cat in tomorrow, it would have been too late." In a way this is also Heartwarming in Hindsight, as it means not only did Doug not cause Stinky's "sickness," he actually saved her life and probably her kittens' lives too by getting her to the vet in time.
