One factor that's involved in guessing the IV's of a Pokemon is whether or not you have powered it up. This is apparently due to the fact that it takes two power-ups to raise your Pokemon one level, but wild Pokemon never half a "half" level.
Just looking at my list, I don't always remember if I have leveled some of my Pokemon up yet. While the difference doesn't appear to be significant, it would be useful to know.
Is there any indicator in the UI that you have powered up a given Pokemon before? (I checked the journal and didn't see anything there).
Best Answer
No, it does not. You just have to try and keep track of it yourself. Looking at the number of candy you have might help though. You could also "favorite" every Pokémon you power up to help keep track. See the following pictures, the Bulbasaur hasn't been powered up, but the Squirtle has.