Finding accesspoints that are offline

Hey guys. I just got responsibility for one of our network controllers with about 370 APs connected. There is also 20 APs that are offline and where I cant find the mac-address on any switch port. We use HP procurve/Arube switches and Fortinet APs. I have tried to get local IT helpdesk to look for the ones that are down but it seems many are moved from the room they were in to new rooms without updating the name (we name them based on room to find them easy). Is there any way to find logs on mac-adresse that has been on a port but is not there anymore? Is there any other trick to finding APs that are down that I might not have thought about? Thanks guys and gals, I always learn something new rom this sub and it has helped me a lot