The way the firmware works it will always use the MAX number of stations and extension boards. If you set a bit on a board that does not exist it will still schedule and “run” that station. So your hardware only has 40 physical stations available, but your device allows as many as 48. So the sbits field you are seeing is correct.
You are also correct in your assumption that station 12 has its bit set, and should be running.
Hopefully that explains what you are seeing,and clears up any worries you may have had about your setup. Just remember the firmware will always work with the maximum stations and extension boards that your particular device is capable of working with. This is done to keep the memory cleaned up and not have to rewrite all of it to adjust for future hardware changes.