Actually there is a bunch of active talkgroups/departments missing in the RR database. My township's (Florence) PD talkgroup is not in there and neither is Cinnaminson's just glancing it at now, and both of those are active. I'd be more than willing to provide updates for what I've heard, feel free to PM me if needed.
I wish there was a listing somewhere showing which talkgroups are on each site, but yes, I am pretty sure that's why. It seems the site that carries the majority (if not all) of the talkgroups is the Westampton/North-Central one. Might want to listen for it in trop DX conditions, as it does get out (was listening to it solid in NW Philly this morning).
I monitor the Burlco TRS from South Philly while at work and from home in Western Delco when the conditions are good. I would suggest a lifetime subscription ($39.95) to Joe Cardani's "Phillyscanner" Ebook. It has a huge amount of info (not just frequencies) on all the area counties, Burlco included. I just checked the database here and would estimate at least 7 times as many TalkGroups are listed in the Ebook (14 PAGES of Burlco TG's!) and they are broken up into the correct sites. The lists are updated regularly and the volume of info is amazing.