Yet more speculation:-
What if Elizabeth Richard(s) of the 1871 Sguborycoed census is not the mother of Sophia Priscilla,William and Lidia Harriet(she would be 50 at the latter's birth),but the grandmother,and the true mother is the untraced Ann(e)
Richards in the grave,giving a birth sequence:-
Elizabeth c.1813,Anne c.1840,Sophia c. 1858
with Ann(e) either being unmarried or married to a Richard(s)?
Regards
Roger