You might be interested in how the authors defined the various subclinical, and euthyroid states in the analysis of their work. It doesn't take too much thinking to drive a coach and horses through their argument and decision making.
1) Only FT4 and TSH was measured. No FT3 anywhere
2) These are the arbitrary ranges and cutoffs for the above
For all studies, the reference ranges were defined as 0.3–4.8 mIU/L for serum TSH and as 13–23 pmol/L (1.01–1.79ng/dL) for fT4. Five clinical strata of thyroid function at baseline were used to classify participants: overt hypothyroidism (TSH >4.8 and fT4 < 13), subclinical hypothyroidism (TSH >4.8 and fT4 within reference range), euthyroidism ( TSH 0.3-4.8, fT4 within reference range), subclinical hyperthyroidism (TSH <0.3 and fT4 within reference range), and overt hyperthyroidism (TSH <0.3 and fT4 > 23).
No prizes for discerning the great hole in their logic. Statistics over personal experience. Arbitrary cutoffs. Also different instruments were used, each having their own ranges - it is incorrect to amalgamate results like this unless you can prove equivalence at all points - which won't happen.
PS Paper lodged with Lyn Mynott for interested people to read at will.