Not positive about this, but...
4 evs=1 stat, correct?
Say you fight 4 bibarels with pkrs=8 evs, but with the power item thats 12 evs(I think)
So in theory when you level up it should say +3, right?
Wrong.
You still gain the evs, however the stats usually dont show up until later levels, like level 100. A level 100 ev trained pokemon is so much more powerful than a un ev trained lvl 100 pokemon.
So all in all, your still getting the evs, but you wont see the stat gain till later on.
Hope i helped