Thomasville, like most of citruses is loosing its thorns when it becomes mature, also each time the mature wood is grafted the twigs contain fewer thorns.
Seeds or no seeds depends on nearby pollination and environment that permits Thomasville to flower several times a season.
I do not believe that there are exist several subclones of Thomasville, just different stages of cultivation.
Thomasville like most of kumquat hybrids has problems when growing on its own roots. Sometime it is seen immediately at seedling stage, but it could also happen lately.
I have for the moment four generations of its seedlings, if grafted on poncirus, they, even slowly growing on there roots, have the same hardiness and fruit quality.