You may want to try to identify the new talk group by searching the STARS system with your scanner. I am not near Division 1 but I don't think I have heard of a Tac 4 in any of the divisions. In looking at the database, Richmond's TG's seem to be 1-16, but I notice that 8 & 10 are not listed. Just a stab in the dark that it might be in one of those, but it could be anywhere in the system.
It would be interesting to search for the TG the next time you heard it mentioned to see what you come up with.