Some of the earlier CWC used a high quality quartz movement which was also used in Omega quartz. There may well be a trimmer on the oscillator of the later models but you would need to open the case to access it. I believe 10 seconds a month is within specification.
Interestingly, Seiko made a King Seiko model with twin oscillators back in the 1970s which is identifiable by a twin crystal logo on the dial. This was accurate to within 10 seconds a year.
Eddie