Dave - despite researching more than 10,000 NAA, AAC/AAF docs I have never been able to find one NAA or AAF Management reference to Apache - only NAA Marketing - and various propaganda illustrations (author unknown) in 1941 referencing Apache.
The few marketing drawings showed six gun wing battery so I I drew conclusions that the origination of the brand was during mid-late 1941 when Kindelberger actually was optimistic that NAA would get an order for P-51s with Materiel Cmd.
Note that A-36 was on the boards in fall 1941 as NAA got wind of the Attack Pursuit funding and knew that Combat command was not excited by A-24, 25, 31 and prototype XA-32.
IIRC the formal 'memo' issued by Materiel Command in 1944 cleared up the various name confusion by declaring that all NAA Variants be named Mustang.