Basically, if you click on a R/B/Y pokedex page, it should display gen 1 sprites instead of gen 6 sprites; if you would click on a B/W pokedex page it should display gen 5 sprites, and so on. The reason why I suggest this is so that players have an idea of how Pokemon sprites were in that generation with a little more convenience. (For the master Pokemon list, the newest sprites for Pokemon should be used)
(sorry, it was hard for me to word this question)