An Approved Device is in my setup any device added to Airwave.
Note that if you have Aruba Instant, the VC will not count for your license, so with a 'single AP' IAP cluster, you see 2 devices (AP and VC), but only 1 authorized device. Also found that I had some stale devices with the same IP as another device, those were not counted either. It may be that there is something with stacked switches as well, but I don't have any in my Airwave.
The numbers for you are quite far off, so it may be good to check with support if you can't find an explanation for the license count that you see.
------------------------------
Herman Robers
------------------------
If you have urgent issues, always contact your Aruba partner, distributor, or Aruba TAC Support. Check
https://www.arubanetworks.com/support-services/contact-support/ for how to contact Aruba TAC. Any opinions expressed here are solely my own and not necessarily that of Hewlett Packard Enterprise or Aruba Networks.
In case your problem is solved, please invest the time to post a follow-up with the information on how you solved it. Others can benefit from that.
------------------------------