There's also a weird thing the GRO does when both parents are named on the certificate but state they aren't married to each other - they index it under the father's surname but with no mmn.
In those instances I'd expect the FreeBMD entry to have both surnames, but perhaps they didn't do that in the early days of civil registration?
Yes but the GRO is not consistent, as mentioned elsewhere my grandmother and grandfather were not married until well after their 4 children were born because my grandfather was already married but his first wife would not give him a divorce.
They had 2 daughters, a son, then the final daughter before their marriage.
The Online Index allows searches under Father's surname only.
The online GRO index adds a line where the mothers maiden name should appear on the first two daughters entries, their mother's maiden surname for the son and it is simply blank for the last daughter.
Their certificates state :-
father's surname and mother's maiden surname for 1st and 2nd daughter;
father's surname however her mother is using the fathe'r surname by this time and that is given plus her maiden surname for the son and 3rd daughter
FreeBMD would not be able to list under both surnames, as they work solely from the GRO indices.
FreeBMD search under both Father's surname and Mother's maiden surname for 1st daughter and show both names on returned entry under father's surname search, but only mother's maiden surname under mother's maiden surname search.
Search on only Mother's maiden surname for 2nd daughter and show only Mother's maiden surname on entry
Search on only Fathe'r surname for son & 3rd daughter, but show both Father's surname and Mother's maiden surname on the entry
Cheers
Guy