For example, in Platinum, you get the pokedex, but at this time it does not record the differences between each gender. You get the upgrade for this just before entering Canalave City. If I had two different gender Pokemon early on (eg, a male and a female Starly) and evolved both of them up to Staraptors before getting the upgrade, would the pokedex remember the differences in appearance of the Staraptors' pre-evolved forms?
[FYI the difference between male and female Starly is the size of the upper-most white patch on its head. In this example would this thing be remembered?]
In the pokedex, it does show the different gender's appearances even the Pokemon's evolved and pre-evolved forms. It shows this in platinum, heartgold, soulsilver, b/w, b2/w2, and X/Y. It would remember the differences in the Pokemon.