need help

[linejudge]

No rulebook handy, so need some help on a couple of penalty enforcements...(NF please). I apologize for the length...

Play 1
A 1/10 on the B10. A's pass is intercepted in the end zone where the player is tackled. After the interception and before the tackle, B55 clips at the B2.

Play 2
A 1/10 on the 50. B intercepts and returns the ball back to the 50. During the runback, B55 clips at the B20.

In our meeting the other night we discussed play 1. We decided that the ruling was B's ball 1/10 from the B10. Reason: The final result of the play was a touchback and regarding plays that result in a touchback, penalties are enforced from the succeeding spot. Since the penalty was marked off from the B20, that is how we got to the 10.
We did not enforce from the B2, as in the all-but-one principal, because the all-but-one principle only applies to fouls by the offense (Penalty enforcement immediately following Rule 10).

Well, if this is the case, then play 2 would also be enforced from the succeeding spot. Because of the all but one. To further complicate matters, the offense remains the offense and the defense remains the defense until the next ready for play (Rule 2, Definitions) so we can't say that the defense becomes the offense because of a change of possession.

Is there a exception or did we miss something. We became very focused on the touchback exception and I am afraid we may have mislead some people. This is really weird because we have always enforced a clip as in Play 2 from the spot of the foul.

Thanks for your input,

Erick