I think that they could just either not address that question or more likely have an explanation as to why these ancient Pokemon are showing up in the present. It wouldn't be too hard, although I'm also not sure if they really care about contradicting any lore.Well, with Galar, it's not like those Pokemon existing in the present day would contradict any other lore. Hisuian Pokemon, on the other hand, would definitely do so. For example, it would raise the question of why we never saw them when Ash was in Sinnoh the first time.
I mean, Ash has gone through entire regions without ever seeing certain Pokemon before, so its not out of the ordinary for him to have missed these.Well, with Galar, it's not like those Pokemon existing in the present day would contradict any other lore. Hisuian Pokemon, on the other hand, would definitely do so. For example, it would raise the question of why we never saw them when Ash was in Sinnoh the first time.