“In a poly/cotton blend or tri-blend with less than 65% polyester, sublimation dye will not bond to the cotton fraction and will wash out, leaving dull, faded color.”

SanMar's 65% polyester threshold is stated verbatim in Source 1, which says that in a poly/cotton blend or tri-blend below that figure the dye will not bond to the cotton and will eventually wash out, giving dull colors and blurry images versus 100% polyester. Source 2 (Sawgrass) never gives a percentage and softens the outcome to 'Lower poly counts give a softer, more vintage finish,' so it does not contradict the mechanism, only the framing. SanMar is the better authority here because it is the only source that supplies the numeric cutoff and the wash-out mechanism, while the Sawgrass page is a glossary written around its own VersiFlex cotton product.