If you have a level 99 Pichu that was properly EV, then you evolve it into Pikachu at level 100, it would have stats.
If you have a level 1 Pichu that you EV train and which evolves at level 2, then you continue the EV training, then raise da new Pikachu to level 100, then the 2 Pikachu, if both have the same EV and IV, would have the exact same stats.
Now if you evolve one into Raichu, then Raichu would be stronger than Pikachu. If both become Raichu, then your Raichu would be the same.
Is it trick ? :D
Hope it help.