Right now, NCPD is operating on their 500 Mhz Encrypted P25 system. If you hear them move over to channel C-x, you know they are off the 500Mhz system and back on the "legacy" UHF channels.
The UHF channels are setup to simulcast their related talk groups on the Trunk System, but it isn't a 1 to 1 match. There will be times where they move to groups that don't have a UHF Simulcast. Another way to tell they are on the 500 Mhz system is to listen. You can 'hear' the digital in their voices. To me, it doesn't sound natural.
I have been logging the 500Mhz trunk system for about 2 years now. I have a PRO-2096 logging with PRO96COM. I would say only 2 - 3 talk groups are not encrypted, and they seem to be used for the radio repair guys.
I have been updating the RR Database as I can tell what groups marry up to what function, but again - hard to do when you can't hear them.
On my website, I have 16 pages of updates that I have logged and others have contributed in one way or another. You may want to start at page 16 and work backwards (I know it is a lot). Here is the link:
http://www.w2lie.net/apps/forum/forum_viewtopic.php?3890