Do many agencies do some sort of TGID equations when converting or is that just a quirk of this particular system you noticed?
I've seen quite a few systems use some sort of conversion scheme. Some, like this one, is the old Type II TGID divided by a number (quite often 16).
Here's another one, down in Southeast Texas.
Original system:
Southeast Texas Regional Radio System (SETRRS) (Motorola) Trunking System Profile
www.radioreference.com
New system:
Southeast Texas Regional Radio System (SETRRS) (P25) Trunking System Profile
www.radioreference.com
After seeing that pattern in a thread discussing changes in that area, I saw the conversion pattern. So, I copied all of the talkgroups into an excel spreadsheet, and converted all the talkgroups, then attached the conversion chart to a post.
I noticed that starting today (11.10.2020) the Jefferson County Sheriff's Office and Beaumont Police Department are no longer on the old SETRRS system. I've checked the new SETRRS (P25 digital) system and they have not been moved there either. Anyone know what the new frequencies are?
forums.radioreference.com
On some of the EDACS systems, that are migrating to P25 (usually P25 Phase II), there's been a number of them where the new ID is the decimal equivalent of the old EDACS TGID, with an added numeric prefix.
Here's an example of that (the old system has not completely shut down; not everyone has moved yet):
Old
Bell County (EDACS) Trunking System, Various, Texas - Scanner Frequencies
New
Bell County (P25) Trunking System, Bell County, Texas - Scanner Frequencies
Look at the S.O. Dispatch.
Decimal EDACS TGID 337
P25 system TGID 50337
So, add the prefix 50 to the old TGID to get the new ID.
There's been others as well. But not all of them follow an identifiable method. I look to see if there seems to be a pattern for the migration. Sometimes there is, sometimes not. When there is, it sure makes things easier to get a jump start on the new system, even before everyone makes the change.