Annabelle says that she knows exactly how everything turns out and that there are no surprises in Heaven. So, why didn't she know Charlie was going to rewind his watch? Because Charlie's not like other animals who get into Heaven: he'll take the difficulty of living over the easy way of the afterlife. Charlie is a surprise. At the end of his song, he even sings it:
Annabelle: What's that you have behind your back?
Charlie: She's gonna be...
Annabelle: Charlie, don't wind that watch!
Charlie: ...surprised!
Annabelle: CHARLIE!!
Fridge-Heartwarming: Charlie's song "What's Mine is Yours" isn't just about establishing his soft spot for puppies. This may also be Charlie trying to teach the puppies to avoid the same trappings as Carface. (From where he stands, if Carface had just been content to share the business with Charlie, things could've turned out differently.) He's trying to teach them that greed doesn't pay, and there's a special investment in generosity. And what better time to teach little ones than with a simple sharing exercise?
Did they imply at the very end that Charlie managed to break out of Hell too? Theoretically the Satan dragon could be in the town merely to retrieve him, but since we don't see Satan running about to pick up the many people that go to Hell, Charlie must have done something to piss him off.
No. He'd already BEEN to hell - after his watch died. Satan was there to make sure he returned after his little visit, but Annabelle intervened and saved him.
Well, that still leaves the question of how he got the chance to go see Anne Marie before Annabelle showed up. If he broke out and escaped back to Earth and Satan showed up to drag him back, that's kind of awesome. If he managed to con/bargain his way into one last visit and Satan was just there to ensure he returned afterwards, that's still a kind of awesome moment for Charlie. Either way, that's fairly impressive.
Another interpretation that could be seen that when Charlie pulled his Heroic Sacrifice by saving Anna-Marie first before going after his life watch, it may have been a good enough deed to earn his way back into Heaven. And even if Satan came for him, the self-sacrifice Charlie made by putting Anna-Marie's life first before his may have been enough to keep him from going to Hell.
It’s possible “Satan” was only taking Charlie to see dying Anne-Marie to torture and punish him.
During the beginning of "Let Me be Surprised", in the background, a lion and a lamb can be seen snuggling together, snoozing peacefully... a clever reference to Biblical passages describing Heaven as a paradise where "the lion will lay with the lamb."
It could also be that when she says "we know everything", she's referring to everything in Charlie's life...the one that just ended. Although it could just be that she hadn't bothered to check past Charlie's death in the book when she greeted him...why would she have needed to?
It's possible she didn't mean omnipotence, but that dogs were just predictable.
Annabelle was also increasingly conveyed as pompous and infallible as well, needing Charlie to protect heaven from one of the angels she entrusted. Saying she knows everything just seems akin to her character.
Not counting the series, the reason Carface isn't in hell during the Christmas Special? After having to endure him for a time, Satan kicked Carface out of hell and restored his life because he got so annoyed with having him around. Now let that sink in for a moment...
Also following that logic, Itchy came back to the land of the living because he missed his pal so much awwww.
Alternatively, perhaps Red handed Carface over to Belladonna, who released him to ensure his loyalty?
Red is a cat, and if hell is akin to the cartoon's canon of heaven, cats likely don't keep charge of doggy hell. And if Belladonna is Annabelle's Evil Counterpart, she likely had rightful charge over Carface. And with Annabelle sending two guardian angels around to help the living, why wouldn't she fight fire with fire?
Fridge Heartwarming: Charlie was so bored and miserable in Heaven because he left behind everyone he cared about when he died. At the end of the second film, Charlie's restored to life, and is doubtlessly going to die, but he'd be with Sasha and Itchy this time.
Additionally, it's made clear he's looked down on by Annabelle and the other more pious angels in Heaven in the sequel, making his social life even more miserable (to the point he's willing to hang out with Carface of all dogs). By the end of the TV series, Annabelle has come to accept Charlie, Warts and All, meaning he has proper friends in Heaven's core circle too.
Characters such as Itchy and Carface being severely softened and having more of a moral compass in later works makes sense considering that in the first film they had not yet underwent the afterlife and what awaits them, likely humbling them a great deal. To compare Charlie ends up needing to learn the same lessons over and over again, since ultimately, being in heaven does little more than bore him.
Charlie in the first film is treated as The Charmer and seems to be quite popular with female dogs. By contrast in the sequel film, Charlie's wooing of Sasha comes off as uncomfortably forceful and does little to win her over. There is a sixty year time gap between the two movies, showing how Values Dissonance has befallen Charlie's way with women.
At the end of the Christmas Special, Carface says he's going to visit his mom. Assuming this is the same Carface from the first movie and not a reincartion his mother is long dead by then, meaning he would be visiting her grave.
If memory serves, the movie implies that she's either died (Careface's tearful, "Mom, I miss you.") or is very old by that point, it's never made certain which happened to her, so she could still be alive by that point.
Of course, since he's now on good terms with Annabelle there's a possibility he can just visit his mother in Heaven either way.
The only way to kill Charlie is by stopping his watch. This is shown during the ray gun scene. Now, imagine if King Gator had succeeded in eating Charlie. The poor dog would have his flesh and organs melted in the gator's stomach and he'd end up being digested...and he'd still be alive during all this.
He was a rotting corpse with a broken back when he first came back until the watch started ticking at which point he returned to his normal living body. Which makes it likely that his body would regenerate if hit by something. Of course this still leaves the horrible possibilities of him feeling "everything" like Wolverine.
Itchy's death by chicken bone in the sequel. Sure, he and Charlie are together again, but poor Anne Marie has now lost two of her dog friends (and probably quite close together, since Itchy doesn't look much older when he shows up in Heaven). Worse, Itchy died after she promised Charlie, who gave his life for her, that she would take care of him. Imagine how much grief and guilt she must be dealing with...
King Gator is not just gigantic, he's genuinely obese. He's eaten so many helpless victims that he got obese from it...
Killer is back to serving Carface in the TV series, supposedly recruited under Belladonna as well. This would imply that Killer died and got his soul reaped by her at some point after the sequel.
Also Charlie, despite being reincarnated at the end of the second film, is back to being an angel in the TV series, only allowed on Earth due to doing Annabelle's duties. Given his reckless nature throughout the franchise, it's not really hard to believe that Charlie kicked the bucket in short time again.
Carface's backstory. As a puppy, his child owner let him take the fall for a mishap and his parents kicked him out in anger. Given the kid visibly was remorseful but too afraid to tell the truth, it leaves you wondering how his own life is if his parents are callous enough to throw a puppy out onto the streets on Christmas.
