National archives site working now, found his service record from 1923 to 1938, discussed with my husband who is ex RN and he reckons Clarence rejoined/was called up again, for WW2 ,as an experienced man, hence not on 1939 register. Records of 2nd world war service are still with the MOD suggest you write to them with full details , his previous service number was J108739 so that might be useful.It would also explain why he did not marry until 1950, he didn't have much shore time!!
Hope this helps.Good luck