Unless something just changed the only MDC being used was on the console side. There's some MDC1200 usage by various radios on Tombstone fire and Benson Fire. Willcox PD and FD is heavy PTT-ID via MDC , but they are on their own repeaters for PD and FD. I did hear them on Fire-East for
As for these "Q' channels. You've really got to stop over thinking and speculating on fire radio usage in Cochise county and in general. This is a generally rural county with only a few actual small cities and towns. There's barely enough traffic to support their 700 Phase 2 systems (money from Buffet's kid paid towards that) let alone all these mystery talkgroups and other channels you think exist. You're probably confusing map grids or sectors for additional radio channels. All of these fire districts have their published, now local use repeaters or simplex licenses still. All they've done is go to a consolidated or unified fire dispatch after repurposed frequencies from the Sheriff's Office.
I've said this before. There's really limited comms needed for fire/ems dispatch, response and status outside of a big working fire. Dispatched, Enroute, On Scene, Returning and In-Quarters is about all you get across the country. There's little if any radio traffic on scene an the guys on the rig or ambo go in together, take care of the call and leave together. They dont need to talk to each other via the radio. The officer on the rig handles the little comms back to dispatch almost exclusively.
Also there's no need for them to be dispatched on VHF and then tell them to get on another radio for a trunked system and keep talking there. That's silly. There's no need and not how things are done. If they want to maintain VHF access say for volunteers or pagers it would be patched back from a trunked system, not telling them to get on another radio to keep talking to the same people.
Not trying to be mean here, but you're spinning yourself into a massive amount of speculation that isn't productive. I'd highly suggest you just listen to Fire-East and West for a while and take a big breath and relax.
