The end of Season 8 sets up the the background of Fray, written 10 years earlier.
When Whistler shows a vision of the future to come in a world without magic, it's clearly the world of Fray, if you notice the hovercars.
Cerebus the Aardvark did this a lot. There were very few minor, throwaway characters. Just about anyone who talked to Cerebus at some point is revealed to be important to the plot somehow.
One of the highest quality examples of this is Don Rosa's The Life and Times of Scrooge McDuck series, which takes every random reference Carl Barks ever made to Scrooge's past and puts together a comprehensive, sensical and engaging character biography. If the Eisner award is to be believed, it really worked.
One storyline of Archie Comics was the result of the events in previous stories: over the past couple of months, Jughead has experienced cranial injury from different objects (box of comic books, flamingo statue, typewriter, football, and a ball of hamburgers). Somehow this causes his body metabolism to go in reverse; wherein usually any food he eats is instantly digested (explaining why he stays so thin), all the foods he eats now turn into fatty tissue, resulting in Jughead gaining a lot of weight overnight.
Sonic the Hedgehog (Archie Comics): During the "Enerjak Reborn" arc, Dr. Finitevus reveals how everything he's done since his introduction has been part of his grand plan to create a new Enerjak. It's also revealed that he was the (at the time) unnamed Echidna scientist who attempted to return Chaos Knuckles to normal by draining his power (the backfire of which is what rendered him albino).
Issue 233: many of Geoffrey St. John's past actions are shown in a new light, as it's explained that he was working on a master plan to make Ixis Naugus king of Acorn.
When the Destructix's backstories were revealed, a bit of this was applied to Sergeant Simian and Predator Hawk. They were shown to, in the past, have been members of the Gorilla Guerillas and the Battle Bird Armada (respectively), groups that were introduced after they were, but before the story arc that revealed their past memberships.
In Non Sequitur, Wiley frequently used three separate sets of recurring characters: everyman Joe and his drinking buddy, Bob, Bratty Half-Pint Danae and Sunday-only character, diner-owner "Offshore" Flo and her tall-tale telling patron, Eddie. Eventually, after years of the characters appearing in their own spheres, Wiley brought them all together: Joe and Bob are brothers, Flo is their mother and Danae and her younger sister are Joe's kids. (Eddie's still just "Eddie").
Rat Queens is split into the original run and the Lighter and Softer retool. Once the retool had its legs under it, writer Kurtis J. Wiebe explained the original run as the alternate universe where the current villain originated. Further, the retool storyline was said villain probing the heroes for psychological weaknesses.
Creators
Alan Moore is famous for re-visioning and changing characters to suit his conception; however he always ensures that the stories preceding his work were given a good conclusion with all background details and subplots resolved so that he can get on and do something different, stating that he does this because readers would otherwise feel cheated that the stories they followed had no payoff.
In Miracleman, a Darker and Edgier reboot of the childish British originals, the bizarre and fantastical Mick Anglo 50s stories are retconned into artificial memories via Lotus-Eater Machine by the Big Bad, ensuring that the old stories had a context and importance to the modern version.
