I was actually wondering the same thing myself, @Shadow Tracker Max xD

While this would never happen, what if only 1 legendary was claimed at one time? So like, Articuno is claimed. And then somehow, without ANY of the other Kanto legendaries being claimed, we go through EVERY other legendary and it loops back around to Articuno. While I can't see that happening any time soon, if we need to I think I will add like some kind of time cap for previous-gen legendaries to stick around for. Like, 2 months, kinda like how Gigi mentioned. x]