As you may know, the sites only broadcast radio traffic if a radio is associated with that site. You could be listening to a site on which a Granite City unit only occasionally registers. From looking at the various sites in this area, the ones that are closest to GC are Edwardsville (site 325) and East St. Louis (site 323). You should also program in the alternate control channels since it could be the primary may be down (they also sometimes switch to the alternate for a few days). Either program the two sites separately and use a wildcard to see what you're getting or put in all control channels in a single group.
FYI, something strange has been going on with StarCom21 in this area recently. Motorola has already taken the Mascoutah, Belleville, and Caseyville sites off line so they may be depending on the St. Clair Simulcast system rather than their own system. I'm guessing that Motorola may also be using the St. Clair system to cover western Clinton county since they don't have any sites in this part of the county. Trying to monitor St. Clair is difficult since our scanners do a poor job of decoding simulcast systems, especially one with as many sites as St. Clair has.