I don't believe there is any sort of a deliberate breakdown beyond the county level. For instance, where I work, radio IDs are issued sequentially with no regard to where the radio is going (PD, FD, EMS, etc.). Its basically first come, first serve. About the only trend I recognize from monitoring is that often times (but not always) console radio IDs are on the low end of things, but not always.
Often times you see a continuous block of radio IDs going to a specific agency because they acquired a batch of radios together. I just picked up some new radios the other day and they were in a sequential block assigned by the IPSC NOC, but the only reason that happened is we got them all together at the same time. Typically, a radio ID is married to it's specific radio's serial number in Motorola Provisioning Manager and it keeps that radio ID for it's entire service life no matter who it eventually ends up with.
For a big county like Marion County, where radios are often passed around throughout the life of the radio, even between agencies and disciplines, there would seemingly be no rhyme or reason to what blocks go to what agencies, especially the longer a batch of equipment is in service.
