RID is global per system. So radio ID 1020 on WV-SIRN is the same radio, regardless of what WV-SIRN talkgroup or department you see radio ID 1020.
Conventional analog systems don't have radio IDs.
Actually not quite true. Analog systems have the option of MDC (or GE-STAR), which would be the "bleep" noise you hear before and/or after a transmission if a department uses it; however, very few if any scanners decode these. There are a few utilities out there which can decode MDC if someone is really into that sort of thing.
It's probably pretty common for the P25 trunked radio ID to also be used on P25 conventional channels, and a variant of it on MDC. For example, 9823212 on P25 trunked could be 9823212 on P25 conventional, and 3212 on MDC.