>>49828185Girafarig, Remoraid and Mareep line are all unobtainable in Crystal, but I would still put all version exclusives in readily available because those kinds of pokemom are meant to be traded across versions. That or you could add a readily available version exclusive tier.
I don’t think counting Crystal as the only valid version is fair if you want to treat the gens pokemon distribution in the same way you would treat other gen pokemon distribution, because this sort of stuff happens on any third version as far as I’m aware.