Understand that PG isn't scouring Varsity or JV stat lines to make invites. They couldn't give one shake if a player has 18 errors (in fact, I'd wager a large sum that they don't have a clue how many errors any of the invitees do or don't have).
Those invites are largely on what they hear from the scouting and coaching community, complimenting what and who they've laid eyes on.
As the kids progress through high school, their rankings and invites change as it becomes more clear who is and isn't among the top in the pecking order. Take a snapshot of the top 25 ranked 2018's and 2019's now and compare it a year from now. The number 1 nationally ranked 2017 prior to that classes Jr. National is now ranked outside the top 100. The more they see and scout, the more accurate it becomes.
If you have or know a kid that you really believes was overlooked and among the top 50 in the country, reach out to PGStaff on this website (Jerry Ford, founder of PG) and let him know. If he can confirm the kid is legit, he may be able to squeeze him in if the kid wants to be there. It is always his goal to have the top kids at the Jr. National and National, regardless of what geography they're from or what events they've played.