That's close, but if you had bet me, I still wouldn't be paying...
7.2.5(a) says:
At the snap at least seven A players, five of whom must be numbered 50 to 79, shall be on their line of scrimmage. B players
may be anywhere on or behind their line...
It doesn't say "shall", "must", or anything like that... It just states that it is permissible... (As opposed to the positional requirements of A...) At best, in only implies what we're looking for... The book has got to be more specific than that...
Plus, there's no way I'm gonna go out and announce the foul as Numbering violation... It just doesn't make sense...