Thread:Tyranitar12/@comment-30294351-20180302190012/@comment-24039980-20180304172744

here's an explanation on the discord channel by Tesla Effect:

Every champion that got short story bios in the client had their previous lore moved to their history pages, since thats is a clear indication that they are getting new lore in the future (which includes the bio and short story, or one of the two).

Some of those short bios even drastically changed the lore of some champions like Fizz and Zilean, one is a Yordle now and the other is an Icathian mage.

So their previous lore is already old....other champions have less drastic changes, but still the short bios are whats going to be part of their new lore.