Currently NPM displays all of the Thin AP's contained within the SNMP message received from a WLC - expected behaviour. However, when an AP goes down, regardless of the reason it is marked as being in an unknown state, and then upon the next poll, if the AP is still down it is removed from NPM altogether.
This just isn't helpful in a monitoring solution. Would it not make more sense to allow us the option of marking an AP as down when it disappears from the SNMP message (unless the MAC reappears on another controller, in which case move it) and then removing it after a defineable period of time such as a week. If there were also the option of manually cancelling an alert (the AP is found to be faulty and has been replaced for example) then this would allow to keep monitoring clean and tidy.