The daughter, Lillian Annie, named on Thomas military papers, I think was adopted when he married her mother ie. NOT his biological child.
Her birth registration is under the surname SMITH:
Lillian Annie SMITH 1909 Llandovery with mothers maiden name KIRKBY.
I have put together a TIME LINE for Thomas CLARKE (from combining children centre records, census and military records assuming they relate to the same man)
Nov 1906 sent from Bradford / Leeds to South Wales
Nov 1907 with Mr John Jones at Plasbach Farm Llandilo
Oct 1908 with Mr John Jones at Plasbach Farm Llandilo
Oct 1909 with Mr John Jones at Plasbach Farm Llandilo
1911 census Thomas with Mr John Jones at Plasbach Farm Llandilo
July 1912 still in Llandilo but different address ( I cannot read place name)
On 24 June 1915, he attests for the military - Living in Ammanford and having just married on 12 June to widow Annie Lilian Smith.
He already had 1 year previous service with Welsh Territorial Force.
28 Aug 1915 He was discharged to an address in Lower Stratton, Wiltshire.
His medical record gives two different reasons for discharge
1. - Curvature of the spine [Tommy does that sound like your grandfather?]
2. - Potts disease of spine (which I understand is tuberculosis of the spine)
This caused muscle pain and rigidity, by was not the result of any military service.
I would suggest that the second diagnosis (Potts) was probably incorrect, as Thomas seems to have gone on to live a normal life.
Dec 1917 when Thomas first received a pension, his address was in St Thomas, Swansea.
1918 married in Glasgow. When exactly?