Hi
If I have the correct census for Sarah in 1901 I note that she lists herself as a widow, however also in the 1901 census it would appear that Edward and Mary Davies the parents of William are still alive, although transcribed as David, and living with them is William, son , single b 1854 Llantrisant - occupation shoe maker, they are living at George St not far from Bull Ring, Llantrisant which is where you found them in 1871.
Edward David Head b 1827 Calstone (I think should be Colwinston) Glam - Woolen Weaver
Mary Wife b 1822 Llantrisant
Thomas son single b 1847 - Shoe maker
William son single b 1854 - Shoe maker
Could this be him???
Will look to see if I can find him in the 1871.
Regards
Z
