Were they identifying the channels as 1##? If they were it would indicate simplex operation. When they operate as a repeater pair they take on a different name. Usually some variant of "L-E" and a number.And today the USCG 6025 was up on CG 113/128 sounding like it is a repeater, CG-113 input to CG-128 repeater, both in the Red and Green, both $293
One thing that leads me to a repeater is a couple of years ago, before the P-25 conversion, Sector Boston had a couple of analog repeaters, one of witch was ID'd on the air as the Deer island Repeater, using 172.3125 with 163.1375 as the input. It's been kind of difficult trying to figure it out as now it is running encryption about 90% of the time.Something else you can listen for is a P25 repeater tail. It's about 1-2 seconds of empty P25 (no voice in the datastream).