Im wondering if a gen V pokemons in Pokemon black and white traded to pokemon HG/SS, and what about the pokedex stat, since gen V pokedex data is not avaible in HG/SS pokedex data.
Pokemon cannot be traded from B/W to HG/SS. The only way pokemon can move between the two games is migrating from gIV to gV, but no pokemon can come back. So, no new B/W pokemon can even get on a gIV game to cause that issue.