So it's probably not worth explaining, but the reason why Yuletide fandoms get commented on as Yuletide fandoms? It's so the bunch of volunteer wranglers can canonise or otherwise sort them as soon as possible after the collection opens. This happens with a lot of collections, including things like Jukebox and other fandoms where mods go out of their way to read the guidelines and approve fandom names that are as close to canonisable as possible.

And the reason why unrevealed fandoms don't get canonised in advance? Would you want to go to an Archive (or a library) and find it has a listing for a specific thing you wanted to find, only to discover the listing is totally empty? No.

Fandoms also don't get canonised on works in draft. Until the work is live, there's no real guarantee it'll ever be live and need an index point for people to navigate to. Shroedinger's fandom.