I unwound it and did it up again.
Uninstalled all A2A planes.
Re-installed one, did the accu-sim update, and modded the add-ons.cfg file as instructed by the A2A site.
Re-installed the rest (after the first was working) and the accu-sim update and the add-ons.cfg file.
My trouble may have started with me moving the A2A planes after first P3Dv4.2 did not show them in aircraft selection. (The add-ons.cfg mod fixes that.)
If you haven't muddied the water like myself... the A2A work around is to edit the add-ons.cfg file in the hidden folder likely on your C: drive C:\ProgramData\Lockheed Martin\Prepar3D v4\add-ons.cfg
In the file, you want to remove the slash at the end... change this...
PATH=F:\Users\yourpcname\Documents\Prepar3D v4 Add-ons\A2A\
PATH=F:\Users\yourpcname\Documents\Prepar3D v4 Add-ons\A2A NOTE: your drive letter may vary