What great finds Hywel, well done. In which Ancestry collection were these? I presume he continued to refuse to pay, hence the 2nd entry. In the first he is 17 and the 2nd 18, so his birth month must be between Jun and Sep therefore born around Jul/Aug 1870. Searching the GRO for James Williams born “Llanelly” in 1870 only brings up 3 entries
WILLIAMS, JAMES mmn LAWRENCE
GRO Reference: 1870 J Quarter in LLANELLY Volume 11A Page 704
WILLIAMS, JAMES mmn THOMAS
GRO Reference: 1870 S Quarter in LLANELLY Volume 11A Page 619
WILLIAMS, JAMES mmn JAMES
GRO Reference: 1870 D Quarter in LLANELLY Volume 11A Page 613
If he was born around Jul/Aug 1870 then the middle one registered in sep Qtr with mother’s maiden name Thomas seems the most likely. You can now get instantly downloadable copies of birth certificates from the GRO for £2.50. If you purchase this it will give you the names of his parents and you know he was in Llwynhendy in 1888, so, hopefully, from this information you will be able to find him in census records.