I had heard from several semi-reliable sources that, upon transitioning to the 700mhz system, talk group IDs would remain the same, for easy transition and simultaneous usage of both RF sub-systems during transition (talk groups would be carried on both systems as needed). My guess is, being largely unfamiliar with Harris P25 specifics, that when a talk group is activated in the system controller ("core" for batwing aficionados), it must be selected as either phase-1 or phase-2, and this selection is forced system-wide, on all RF sub-systems. This would create a problem for York County, since 500mhz terminal units are almost exclusively phase-1 only, and the 700mhz RF sub-systems have half of the channel capacity as the 500mhz side. A phase-1 selection would overwhelm channel capacity on 700mhz, and a phase-2 selection would disclude legacy subscriber units. Loading 700mhz users onto new talk groups specifically on the 700mhz side would eliminate the system trying to force talk groups across the two bands (and phases). Maybe this isn't the reason. I don't know. Maybe a whole new system controlled was installed. No, this couldn't be the case, since this was just an "upgrade" and not a new build-out.
I do know that users using the 500mhz side can no longer monitor users who have transitioned to 700mhz talk groups from their existing terminal units, and vice versa. I can't speak to interop between the two disciplines (police to fire/EMS), because we aren't told if there are any talk group that can be accessed from both RF systems in the event of a full-scale incident or even routine interop. Many EMS agencies historically monitor their respective police agencies' dispatch and chit-chat talk groups for reasons that should seem obvious. This can no longer happen.
Field users are uninformed, changes and implementation is occurring in illogical order, and, while day-to-day function is mostly routine (with small changes), it's inarguable that the full benefit of a county-wide system is currently intangible in the current state of transition. I'm sure the suggested answer if such an inquiry were made would be some sort of console patch. Because, in 2017, console patches WITHIN a single P25 system seems perfectly reasonable for critical incident interop.
But what do I know, I'm just a paramedic.
EDIT: I'm guessing that, since DCR_inc mentioned ISSI, that there are two controllers running. Still not sure if two RF subsystems connected by ISSI must choose a global modulation, or if each RFSS can operate in it's own.