People do not always marry before the first child. Some take somewhile to get around to it, if they do at all. It is possible however William was a widower on his marriage in 1891. You won't know until you either find the marriage in the parish register or purchase the certificate.
You know from the birth certificate Joseph's mother was Mary Townsend and you know from the 1891 census she was Mary Ann Townsend.
The marriage details from the 1891 marriage will hopefully confirm it is the right William (e.g. from his occupation) and give you the names of Mary Ann and William's fathers' and their occupations. Trying to track back a Smith it is very important you have as much information as possible. With Mary Ann since her birthplace is actually unknown - All Saints Worcester, Bath, or somewhere else, you really do need her father's name as well, as either the 1891 or 1901 census is wrong about her birthplace (and of course it could even be both). If either/both censuses are slightly out on age for William or Mary Ann it makes it even more likely that you are in the realms of speculation and accumulating more and more possibilities in earlier censuses, but nothing that anyone can actually be sure of. Searches in earlier censuses would be far more fruitful with the information from that marriage.
The 1881 census has two William Smiths - bricklayers (but not bricklayer's labourers) living in Worcester (and your William Smith could just as easily have an occupation given as a labourer). One gives a birth date of circa 1864 - track him back to 1871 and his birth year is circa 1857?? Which emphasises the need for father's name to try and pin it down.
I have seen Martha/Mary Ann being confused before on censuses. Without another census entry for her it is impossible to know which is right.
Regards
Valda
