I'll have to find the origin of that chart from Coats, because it doesn't make sense to me. Tex is supposed to be fiber weight in grams per kilometer. The chart shows weight and Tex going in different directions.
Maybe you had it right in your previous post, that I misunderstand what T26 and T67 labels are. Funny that a top hit file when you search on thread weight is a paper on the several systems from Coats which tells you that Tex is straighforward. But, then I find another file, also from Coats, which includes the "Ticket" system. Yeah, another "T", and that article has a correspondence of Tex and Ticket, going in opposite directions. So maybe one T26 and T67 are both from different "ticket" systems.
Nothing wrong with Clark thread if it is quality. But, I remain confused about what I have.