Those must be small systems. I don't have anywhere near 120 systems and I am over 20%.I don't think your memory will be an issue. I have 120 systems and a bunch of IDs programmed into my BCD996XT and am using less than 20% of the memory.
I have also read where some systems use a fail-safe backup system where all the frequencies are used in conventional mode, however I have never experienced this first hand.
While remote, there is always the potential for a trunked system to use a voice frequency as a control channel, unbeknownst to the the database. If that happens, you will miss comms.
Adding all the frequencies should have no impact on the scan speed as its only going to scan control channels.
This is not true. The control channels (and alternates) are programmed in the user radios. They cannot use voice channels as control channels. They can only use the pre-defined control channels (Primary and alternates).
Adding the voice channels mean an increased chance the scanner may lock onto a distant trunking system should that one happen to use one of those voice-only channels as a control channel on their system. That means you will no longer be trunking the system you want, but a different one.
There are several reasons for not adding the non-control channels, but no logical reasons to add them. As I mentioned, the user radios only have the control channels (again, Primary and up to 3 Alternate) programmed in them, and like the scanner they use only those to trunk the system.
So if this is an issue, why does Uniden download all of the frequencies for sites rather than the primary and alternate control channels and then "push" them to the Sentinel database?
This is the rule of thumb I have gone by for years and I can't think of a single time where it ever resulted in a problem of any kind. I suspect Uniden pulls all the frequencies from the database to Sentinal for the same reason. I know of a number of P25 systems that regularly change control channel frequenciesThe point that ofd8001 was probably making that the some of you are ignoring is that you are assuming that radioreference has 100% accurate information for all the trunked systems in existence, which is not a true assumption to make. Yes, the ONLY frequencies you need to program for the 996XT to function correctly are the control channels, but not every TRS listed in RR has every system 100% correct. Therefore you are better off programming all listed frequencies for any TRS that is questionable. Unfortunately figuring out which systems in the db are 100% correct can be as frustrating as figuring out which posters in the forum give credible information.