Agencies get new radios all the time. The Assistance to Fire Fighters Grant's were awarded a few months ago, I believe, so don't be surprised when you start seeing new FD's on 800, or new RIDs. I've seen some users go through 2 or 3 RIDs in the past 2-3 years. RIDs can change when new vehicles are issued, old vehicles are decommissioned, vehicles get in crashes, people change positions within a dept, etc... it's not uncommon to see new/undocumented RIDs weekly.
However, if everyone has new RIDs, including dispatch, then you're talking about hundreds of radios, which would be newsworthy, so check the local Gov't news briefs for grants or radio system upgrades articles.
Everyone getting new radios on the same day doesn't happen either, it takes time to flash or install radios in every vehicle and in dispatch, plus there will be on-air testing, so if everything changed all at one time, then it's likely a SNAFU on your end somehow.