The 2011 AR refers to 10-2-2-d-2-(a), which is confusing, because, 10-2-2-d-2-(a) requires the change of possession to be in the end zone, but in the play situation (both the AR and BCTGP's original post), the COP is in the field of play.
As we must do on the field, when I first read this post, my initial reaction - without looking at a book - was that the goal line would be the Basic Spot, and the penalty would be enforced from there, to the B-10. But the touchback by pure result of the play would be better, so decline the penalty. 10-2-2-d-2-(b) supports that.
But, the AR (2011 Bulletin 4, play 3) conflicts with that. If we, as a crew, recalled the AR, then we would have little choice but to follow the AR, and let somebody else tell us we were wrong (or right).
Note that the 2011 rule language and the 2018 rule language are virtually identical - the only difference being that the words "Succeeding spot" now appear, in lieu of "20-yard line," at the beginning of 10-2-2-d-2-(a), because of the change in the kickoff-touchback rule implemented a couple of seasons ago. So, we aren't dealing with any rule change since 2011. So, what's a poor slob to do? Follow the AR, I'd say. B, 1/10, B-30.
If the interception was in the end zone, easy. 10-2-2-d-2-(a) covers that explicitly.
But, with the interception (or any other COP) in the field of play, that would seem to be covered by 10-2-2-d-2-(b), with which the AR is in direct conflict. The only possible explanation would be that, somehow, somebody is saying the change of possession occurred in the end zone. But, by virtue of the fact that, if the interceptor fell to the ground in the end zone with the ball, we'd give him momentum, and place the ball at the B-3, that clearly means the COP was in the field of play.
Change the rule, or change the AR. I don't care which. But please clarify for us.