I'm still working on updating current rosters via JSON file and I'm having following issue:
There seems to be a limit how many players per position the game loads up. I have about 180 REAL players playing Tackle in my JSON file but when I load the game up only about 130 shows up. What's worse there are about 50 regens (fake players) playing Tackle added to my game. Am I doing something wrong? The same goes for other positions too like TE and QB....I've been working on adding realistic NFL roster mode and I only want to see players that are in my JSON file not bunch of Regens. Please advise.

It should be loading them all... there isn't any limits where it starts ignoring players. If you don't have enough then it will add filler in.

Ok, I figured it out. In JSON file in column BT(Redshirt) I left the cells blank for some players and that's why they didn't show up in the game. All cells in that column should be set to FALSE. No idea what it means though (Redshirt)...