Well, maybe you aren't smarter than that...
Talking about single carrier status has nothing to do with M-B, which is only about integrating employee groups. The UA/CO example was used to illustrate that single carrier status can be granted by the NMB long before there's a single ops certificate, combined seniority list, or combined contract. Nothing in M-B changes that. So APA could request a single carrier status ruling from the NMB prior to seniority integration and such a ruling would trigger a representational election. Assuming APA would win that election by virtue of having the numbers on it's side, then it would be in control of the seniority integration process (within it DFR responsibilities and M-B ).
You're mixing up two different things, or are just mixed up. One is which union would represent the combined group and when they could become the sole representative - that's the NMB's responsibility. The other is seniority integration, which would fall under M-B - the NMB could care less about that.
Jim