Just to expand on what brian said; After awhile you get a general feel for a player's final OVR rating based on his age at signing, initial OVR, and make-up. (Of course, injuries can throw all that out of whack.) Then, depending on how much money you have in your scouting budget, you can decide on how much you can believe the projected OVR. For example, if you have $20M in college scouting and draft a college player, you can feel fairly confident that he will get close to the initial projections (barring injury, manager stupidity, etc.)
You've been around long enough that you should be able to start getting a feel for things. But you'll never get a true feeling until you remove your advance scouting crutch. Like riding a bike, you'll never learn how to ride a bike until you take off the training wheels. Getting your advance scout budget down to zero frees you up to do a lot more with your budget.