It may be their marriage was never recorded and then there is the possabilty she may not been his wife .The latter is true in my case. My grt-grt-grt-grdfather was supposed to have been married three times but I have only ever been able to find records for two and then the woman show to be living with him when,at his death,that is identified as his "common-law" wife is actually his grddaughter from first marriage . A lot of early census are not too accurate in some details .