When we were still utilizing Citadel music formats, we had our XDS, with one port for ABC Entertainment news for station A, second port AC format for station B, third port Hot AC for station C, and fourth port generic ABC news used by station B and station C. AFter we stopped using Citadel music formats, we were able to use second port for talk programs on station A. In that case, the station B call letters were still assigned to that port. Any one of those ports can be station-specific, and the network can regionalize spots or spot tags all the way down to a specific station, as I understand it.
I don't know if this relates to what test123 was referring to, but if I wanted to, I could program the XDS even now to receive, for example, Doug Stephan's Good Day, on any one of the ports, although they are identified for different stations, and if the network wanted to run a spot on KBKW, for example, and I was running the program from the port for KJET, then we would air the wrong network spot.