« Reply #9 on: Thursday 06 June 19 22:42 BST (UK) »
the 1871 I'd found with no Margaret isn't the correct family as tracing them matches to a certain Jones family using Gower as a middle name. And the Thomas of that family doesn't have the same siblings as in 1861.
There is this entry in 1871
93 Dillwyn St, Westfa RG10/5465 folio 99 pg 20
Thomas Jones widower 35 moulder at iron foundry b. Llanelly
He married Catherine Jones sept qtr 1872 Llanelly vol 11a pg 1023
76 Dillwyn St RG11/5372 folio 125 pg 4
Thomas Jones head mar 45 moulder in iron foundry b. Llanelly
Catherine wife 36 b. Llanwrda
Edwin son 8 b. Llanelly
+ 3 boarders
There's this 1851 census entry with Thomas and siblings that match the ones in 1861
Blaen Lliedy, Glyn HO107/2469 folio 243 pg 7
William Jones head mar 46 carpenter & farmer 60 acres b. Llangyndeyrn
Mary wife 42
Thomas son 16
Margret dau 15
William son 14
John son 12
David son 10
Mary dau 7
Rachel dau 5
Daniel son 3
Sarah dau 8 months
Eliza Davies grand dau 8 months
all born Llanelly except William senior
Another possibility is that Thomas died early. Possible for widowed Elizabeth/Betsy
1871 Cottage Plough, Glyn RG10/5471 folio 9 pg 11
Elizabeth Jones head widow 32
Margaret dau 10
William son 6
all born Llanelly
1881 Plough no 2, Glyn RG11/5378 folio 10 pg 14
David Roberts head mar 46 coal miner b. Llannon
Elizabeth wife 42 b. Llangendeirne
Margaret Jones dau 20 seamstress b. Llanelly
William Jones son 16 labourer at coal works b. Llanelly
Mary Ann Roberts dau 9 b. Llanelly
Joseph son 7 b. Llanelly
Jane dau 4 b. Llanelly
marriage reg dec qtr 1871 Llanelly vol 11a pg 1096
birth regs
Mary Ann Roberts march qtr 1872 Llanelly vol 11a pg 705 mmn Williams
Joseph Roberts june qtr 1874 Llanelly vol 11a pg 834 mmn Williams
2 possible birth regs for Margaret with mmn Williams in june qtr 1861
marriage reg
Thomas Jones & Elizabeth Williams june qtr 1860 Llanelly vol 11a pg 817
This seems more likely scenario.
Cornwall: Allen, Bevan, Bosisto, Carnpezzack, Donithorn, Huddy, James, Retallack, Russell, Vincent, Yeoman
Cards: Thomas (Llanbadarn Fawr)
Glam: Bowler, Cram, Galloway, James, Thomas, Watkins
Lincs: Coupland, Cram
Mon: Cram, Gwyn, John, Philpot, Smart, Watkins
Pembs: Edwards (St. Dogmael's)
Yorks: Airey, Bowler, Elliott, Hare, Hewitt, Kellett, Kemp, Stephenson, Tebb