I know a young man who scored a 6.5 at a PG Showcase. He was 14.
Nine months later he made unofficial visits to (2) ACC schools and an Atlantic-10.
Still uncommitted, but you get the point.
I have to laugh..........while posting on another thread regarding the Cape League, I mentioned a young man I remember who was an LHP at a D-3 NESCAC school and managed to get himself a roster spot in the Cape Cod League in 2011. Played for the Chatham Anglers.
Summer before his senior year of high school his range was 74-76mph. PG gave him a grade of 7.0.
FOUR YEARS LATER HE WAS PITCHING IN THE CAPE LEAGUE. One year after that, he signed as a free agent with the Arizona Diamondbacks, and later pitched in Orioles organization. He retired in 2014 and is now putting his NESCAC degree to work.
As Bucsfan stated, a PG rating is "just a point in time."
And if you look at the PG definition of a "7" it reads "College prospect, possible future draft pick with development".
I think most people are putting way too much stock in a rating and assume that a 9-10 is a guaranteed draft pick or D1 freshman starter and anything 8 or below is lucky to play after high school.
Like you state, it's a snapshot in time and whether a player grows or shrinks from there is dependent on a lot of variables.