I thought the NFL bag was just for the stats guys in the pre-video days.
As an NFL stat guy, I can tell you we NEVER use the spot of the beanbag, it's nowhere near accurate. It's typically thrown by a deep official who is well ahead of the play (as he should be), and he is throwing it a significant distance. If he gets within two yards it's a good throw.
But the bag is more important than that. The spot of the interception can be an enforcement spot.
PERSONAL FOUL OR UNSPORTSMANLIKE FOUL BY OFFENSE
Article 3 Personal Foul or Unsportsmanlike Foul by Offense Prior to Change of Possession.
When the offense commits a personal foul or unsportsmanlike foul prior to an interception, or the recovery
by the defense of a backward pass or fumble, a 15-yard penalty will be enforced from the dead-ball spot.
Exception: If the intercepting or recovering team loses possession after the interception or recovery,
enforcement is from the spot where the interception or recovery occurred, and the ball will be retained by
the intercepting or recovering team after the enforcement for the personal foul.
A.R. 8.50 Third-and-10 on A30. B1 intercepts a forward pass at the B30, runs to the B35, fumbles and Team A recovers.
Prior to the pass, A3 crackbacks on A26.
Ruling: B’s ball first-and-10 on B45.