One of my favorite ideas from Morrison's Batman run was that the entire history of the character from Detective Comics #27 onwards happened. It mattered. It's all part of the character's DNA. He doesn't just reference that numerous times throughout his run in flash backs and flash forwards, but he takes bits and pieces from Batman's entire comic history(including the parts readers tend to forget or even embarrassed by) and he embraces them, like the Batman TV show of the 60s or the Club of Heroes from the 1950s. The different styles and tones and story structures throughout his run demonstrated how versatile the character of Batman is, in that you can fit him into any kind of adventure and he still works.
"Detective #26" goes one step further and says that even the comics BEFORE Batman's first appearance are canon as well, and they are a part of his legacy. The story's point of view is filtered through the Silver Ghost, who on one level isn't too far away from the Grey Ghost, the vigilante who inspired Bruce in the 90s Animated Series. But on another level he's part of a generation of pulp heroes who evolved out of the old hero archetypes, the type of characters who can have many adventures again and again. Characters such as Zorro, the Lone Ranger, Doc Savage, The Shadow, The Phantom, and Sherlock Holmes were created because it made a perfect story vehicle for more content. You don't have to invent a whole scenario and reason for why Sherlock Holmes gets involved with another mystery; his whole reason for existence is to keep finding more adventures to get into.
And then comes Batman, breaking through the window in Detective Comics #27. The Ultimate Synthesis of all those hero characters. The jack of all trades. He's James Bond and the Shadow and Indiana Jones and Sherlock Holmes all rolled into one. He's not just a hero; he's a Superhero. And he, and the entire lineage of superheros that followed, immediately and irreversibly rendered guys like Silver Ghost old fashioned and irrelevant. After Detecetive Comics #27, how can you go back the old guys? The way Sherlock Holmes and the Lone Ranger replaces the random cowboys and detectives of genre fiction, the Batman has replaced them. And his character has proven so versatile, that in the 80 years since, nobody has replaced him.
It's a very fun, meta coda, both critical about the superhero domination of genre fiction but also celebratory of Batman's longevity. A perfect short story for an anniversary issue and plays excitingly well with Morrison's big themes about the character.