Hello

I think that Thomas David on 1851 at Old Road with wife Anne are still on 1861 and 1871 in the same area, although Thomas's occupation has changed.
1851
Thomas David Head age 47 born Llanddarog Farm Labourer
Anne David Wife age 57 born Llanddarog
Betty David Dau age 18 born Llanddarog Shoe Winder
John Evans Nephew age 20 born Llanddarog Journeyman Smith
RG8 Piece 2465 Folio 557 Page 34
Could be them at 1861 Weig Road
Thomas Davies Head age 55 born Carmarthenshire Haulier
Ann Davies Wife age 69 born Carmarthenshire
William Evans Lodger age 23 born Carmarthenshire Smith
RG9 Piece 4100 Folio 40 Page 44
and 1871 at Middle Road
Thomas David Head age 70 born Llanddarog Labourer in Tinworks
Ann David Wife age 80 born Llanarthney (next Parish to Llanddarog)
RG10 Piece 5449 Folio 29 Page 55
Occupations did change at this time due to the move away from rural to industrial society.
What do you think?
Best Wishes
Morgan