Dunno how is it with the migration of built-in AP license, but for the AP/AAP difference see here:
https://gtacknowledge.extremenetworks.com/articles/Q_A/What-are-the-differences-between-AP-and-AAP-on-WiNG-v5-x/
I don't see in some internal doc that NX would get AP licenses, just AAP, so if you were allowed to migrate 6 AP licenses to NX by Extreme rep's, it would be migrated to AAP license IMHO.
KR,
Tomasz