Hi
Have tried to look at this in another way.
What do you think on this-
looking at the 1871 census Rg10 5469/11/16
Colliers Arms Pembrey
William Jones b 1850 llanelly carmarthenshire coalminer
margaret Jones b 1848 b kidwelly carmarthenshire
sarah Janes daughter b1870 4mths old Pembrey
the above info matches your 1881 census info
There are two possible births
Given that they say sarah jane is 4mths old
sarah Jane Jones 4th qtr 1870 vol 11a page 595 llanelly
sarah jane jones 4th qtr 1870 vol 11a page 603 llanelly
(Census 1871 taken on 2nd April)
poss address time of birth Colliers Arms Pembrey
so there is a long shot that one of these girls where born at that address, bad luck if both have fathers William but good luck if only one has mother margaret.
Possible marriages
William Jones =m= Margaret Jones 4th qtr 1869 vol 11a page 937 Lanelly
(if wedding was not a shot gun marriage this is the marriage I would go for) Bad news if there are more Jone's!
William Jones =m=Margaret Davies 3rd qtr 1870 vol 11a page 861 llanelly
It can work in looking for a sibling then you are able to piece together who you are looking for. I have done this myself yes you
end up with two birth certificates but its in the same family.
its worth a shot.
I hope this has helped you have fresh eyes on your family search
cheers cardiff