You have to work with the info you're given.
Once you sign a player, his projections do not matter. At that point, you develop him. If you're not trading 2nd/3rd year players, projections don't matter. If you're trading 4th year players, they are pretty much what they're going to be.
I use SIMMY recs to start the season and adjust as the season progresses. A pitcher will throw about 15 pitches per inning so, if I want a RP to throw 2 innings, I'll adjust to 25/30 if SIMMY recommends 30/40.