Yes they transmit sometimes in analog and sometimes in digital, its hard to tell why because I have heard them actually working a case in "normal" mode and sometimes they use digital for no apparent reason at all. Have fun monitoring TPD.
I have been on lay over in Tuscon on more than one occasion and actually submitted some info on this back a while. It may have changed but I can confirm as of a couple years ago they transmit both analog and digital. The few days here and there I was in town didn't let me figure out more than PL and NAC codes for the channels but they would be analog one second and digital the next.
I don't know if they have something like this or not but if they do then this might be it. Could the radio automatically transmit in the mode last heard on it? So if someone transmits digital the next user would automatically do the same when keying up etc? (or some version of that) Some units might be manually set to either too if its possible rather than an auto response.
Don't know about migration but they've been doing it this way for some years now.
TPD has analog and digital capability for some users. Detectives and SWAT, for example, have the capability to swith to the "cyphered mode" or "8C" for example. The use of the term "cyphered mode" should not be confused with encyphered comms, as some of the TPD users believe. It is simply the term used for the digital mode of the radio. All transmissions are currently monitorable with the proper scanner.
P25 radios have the ability to receive both analog and digital transmissions on the same channel, but can only be programmed to transmit EITHER analog or digital on that channel. That receiving status is called "mixed mode." For example, if the dispatcher wants to transmit a wanted status for a person then the transmission might be done in digital, and unless the listener had a P25-capable receiver the listener would hear only "hash."
While doing some clean up on the database, I realized where the confusion is coming from. I've added the separate entries for TPD F7C, F8C, F9C, and F10C. This should help differentiate when they are digital vs analog. Sorry folks