Most departments now will not be so forthcoming with frequency information like they did in the past. About 30 years ago when I worked for a Sheriff's Department in Kansas, we actually have a paper that we would give to anyone who asked (as long as we knew they weren't a dirtbag) that had all of the frequencies for all of the law/fire/ems in the county as well as KHP and Point-To-Point frequencies so they could take it to a Radio Shack and get the right crystals. We even went so far as to help put the crystals in if need be. The Sheriff at that time was a big proponent of having citizens listening to scanners as they were able to assist us in locating vehicles, individuals, etc.
To you point however, it is much better for you to derive this information on your own. First thing to do is to print out a listing of your county from the database and begin to verify that all of the database listings are correct. Check frequency, tone and usage for each listing in the county and check off that listing when it is confirmed. Next thing to do is look at the callsigns used by the agencies and look them up on the FCC web site to see if there are any other authorized frequencies for that license grant. If there are, program them in and listen for traffic on them.
The information is out there to do what you want to do, you just have to look for it. When I did this for my county, I found several errors that were submitted to RR for the database. Part of the fun is in the hunt!
Dennis