How to divide the NFL players’ number?

NFL players’ numbers are divided by positions of the players:

1-9: Quarterback, Punter and Kicker;
10-19: Quarterback, Punter, Kicker and Wide Receiver;
20-49: Running Back and Defensive Backs( Cornerback and Safety );
50-59: Center and Linebacker;
60-79: Offensive Lineman( interior offensive line ) and Defensive Lineman;
80-89: Wide Receiver and Tight End;
90-99: Defensive Lineman and Linebacker.

NCAA stipulates that offensive linemen must in the number of 50-79, quarterback and running back should use the number under 50, wide receiver and tight end use the number more than 70, and the number 90-99 leave to defensive players. In this way, the NFL official organizations can identify the player whose number from 50 to 79 is the offensive without a ball.