One of the biggest debates in the world of DXing is whether or not to count a call letter change as a separate station. There are reasons for and against counting a call letter change.
In my experience, the reason I have for counting a call letter change is that regardless of whether or not the said station has a new owner, the philosophy, programming policies, air talent (if they have any) and/or type of programming offered with the call change. Usually, a call letter change is connected with a format change; occasionally, it would also be connected to an image change if they stick with the same format. If, for instance, KXFN 1380 returns to its original call of KWK and broadcasts a different format from its previous sports talk format; say, for instance, a brokered ethnic format, then I would count that as a separate station. Even if that station changed calls and retained the sports talk format, I would still count that as a separate station. Numerous DXers won't count call changes on the AM (medium wave) broadcast band; this is the only band where I count call letter changes. In my log, it is marked with a "CC" in the parentheses. In my chronological and frequency logs, it's noted this way: "KWK Saint Louis, Missouri (CC)". In my geographical logbook, organized by state, I would mark the log this way: "KWK-1380 Saint Louis (CC)" That way, DXers can take note of the call letter change when looking at a printout of my logbook, and take that away from my totals if they don't count call letter changes in their own logs. A city of license change on AM is marked with "CLC". For example, if I logged KSTL 690 from Saint Louis, MO, and since I last logged it, the city of license was changed to East Saint Louis, IL, I would mark the second log in my chronological and frequency logs this way: "KSTL East Saint Louis, Illinois (CLC)". In the geographic (by state) log, I would mark the second log this way: "KSTL-690 East Saint Louis (CLC)".
However, I do not count call letter changes on FM, TV (analog and digital) and NOAA Weather Radio, in accordance with the standards set up by the Worldwide TV-FM DX Association, the primary DX club dedicated to VHF and UHF DX. In the view of many DXers, it's the physical plant of the station they're concerned with. It's the same transmitter site; many times, it's the same studio location (if the station is part of a multi-station deal in that same market). Programming policy and philosophy, air talent (if that applies) and type of programs aired do not count. So, for example, if KNOU 96.3 Saint Louis, MO and KPNT 105.7 Collinsville, IL trade places on the dial, I would not count these stations separately if they switched frequencies (96.3 would be counted as KNOU, not as KNOU and KPNT, for instance). It may get murky with digital TV, however; I have logged digital channel 19 in Des Moines, IA as WHO-DT. I also have WHO-DT logged on digital channel 13. Would I count digital 19 separately if I logged KDMI? I would also count a city of license change; for example, I've logged WWF44 162.500 with the transmitter in both Fort Payne, AL and nearby Henagar; it's the same with WXL47 162.400, having logged the transmitter in both Dexter and Bloomfield, MO.
While I adhere to one standard for FM, TV (analog and digital) and NOAA Weather Radio DX, I have pretty much set my own standards for logging AM (medium wave) broadcast band DX. I'm sure you have your own standards, when it comes to counting or not counting call letter changes.