This is a very interesting discussion but, as Bum's very cogent discussion implies (to me at least), one can't reliably infer from Perfect Game's spectacular database what any given individual will be able to do.
For me, one of the most useful and practical questions that Perfect Game data can answer is: Given the wide range of program levels within, say, D-1 category (i.e., ~300 colleges/universities are listed as NCAA D-1 baseball programs) what are their average expectations of some measurable performance level for High School-aged prospects?
For HS-aged pitchers who participate in a PG event, their database pretty reliably gives a radar-measured peak FB speed. Sometimes there is anecdotal information or some quantitative data about other pitches, but majority of the time it's just top FB velocity.
How can one use this data in a meaningful way? Here is one example: I was interested to know the average FB speed in High School of RHP prospects who eventually made it on to a WCC conference roster in 2012. A different way of stating this is: I was interested to know what type of performance level WCC coaches expected, on average, from their HS RHP prospects.
To answer this specific question, one needs to go to the roster page of each individual WCC school and make a list of all the 2012 RHPs on those rosters. Then, cross-check the list against PG database by searching each individual name at the PG website.
Without question the exercise is tedious but if you really want to know what the average expectations of coaches are for recruiting HS players into their conference I think that approach gives about as realistic an answer as possible:
HS-aged RHPs who eventually found their way onto a WCC roster in 2012 threw the fastball during high school with vel = 86.5 +/- 3.5 mph. Thus, about 70% (1 std. dev.)of these eventual WCC-level RHPs were in the range 83 - 90 mph when they were measured by PG during their High School years. Another 15% of them were higher than 90 mph, and yet another 15 % of them were lower than 83 mph when the measurements were taken.
For LHPs who eventually appeared on a 2012 WCC roster, the average HS velocity was lower, as one might expect: 84 +/- 4 mph.
One can perform this analysis for any single school, or any conference, as long as there is sufficient data for in the PG database; however, there is a caveat: Very weak programs generally have many fewer pitchers with PG data available, strong programs seem to be stacked with more players who do have PG data...it seems natural that strong players would not only be more active in showcasing themselves but would also of course tend to populate the stronger college programs. So the analysis is much higher quality for the upper 2/3 of the ~300 D-1 college programs.
Another example: The data for Pac-12 conference, which obviously includes many nationally high-ranked programs, shows that the average expectation for a High School-aged RHP fastball was 88.7 +/- 4 mph, a range of 84.5 - 93 mph for the 1 std dev group.
None of this data-crunching pretends to tell any individual how he is likely to progress in HS or beyond. As Bum implied, that depends on factors that are impossible to measure with a radar gun. However, perhaps what it can do, with the best quantitative information available, is guide a High School-aged individual toward setting realistic goals based on the evidence for coaches' average expectations at the various levels of college baseball.