It sounds like you are appending these from the main database. Is that correct?
For the "systems" that you are adding, are these actually the departments in use on the system? When you append a large system like
TACN to a Favorites list in Sentinel. you can select only the departments you want, and append only those. However, in Sentinel, doing that also appends every site as well, because Sentinel does not know which site the talkgroups you selected are carried on.
If you remove the excess sites (those well out of range, for example), then you've ended up with specific departments, and just the sites you wanted. However, if you change the name of the appended system, from the name used in the database (Tennessee Advanced Communications Network (TACN)), to, say TACN Chattanooga. then try to add another department to that, Sentinel does not recognize it as the same system, so you get all those extra sites (that you did not want) again, into a new system named like the original before modification, Tennessee Advanced Communications Network (TACN).
However, I've noticed in appending systems of interest in my area, that if I do not change the name, then I can append one or more additional departments to the system, without the excess baggage. But if, instead, I cut the name down to size, or to something more specific to what I want to add, then if I try appending another department, Sentinel then sends all the sites once again. I verified to myself, that if I were to change the name of the system back to what matches the main database, then I can pick & choose specfiic departments without getting sites I do not want.