Ref your reply 7. There are numerous posts on Rootschat where children are registered in the man’s surname but the couple never married. In doing so - one of 2 things can happen on the birth certThe mother is shown as Susan Gadney nee Wells - giving the impression the couple are marriedThe mother is shown as Susan WellsDo you have a copy of either of the first 2 children's birth certs?Logic dictates that if they were married - why would she be referred to as Wells in relation to the assault charge in 1840?
There are known to be entries missing from the GRO index, which you can report from the foot of the search page. Your reason for believing it to be missing would be that it is in Ancestry. Have you checked FreeBMD as well?