Welcome, Steely Dan, to our forum. May you find it both enjoyable and informative.
The rationale behind the list of spot fouls by A behind the line of scrimmage is the foul could be intentional to prevent loss of yardage more than the penalty would cause ifenforced fro the previous spot. Example: A's ball @ 50, QB scrambles back to his own 40, about to be sacked he spikes a forward pass. Previous spot would place the ball at A's 45, which wouldn't be fair. Hope this helps.