100% cotton label, 100% not cotton

I feel so gaslit trying to find 100% cotton shirts. So very short story my partner hates and I mean hates not cotton shirts. He intentionally will only buy items labeled as 100%.

However every time in the past 1-2 years he orders say a band shirt or even official sport merchandise. And he buys the 100% cotton it will come in, the label will say it's 100% cotton and it flat out is not.

This latest culprit says is 100% and it has more stretch than my 97% polyester tank top. The material looks and feels completely different from cotton.

He has always preferred cotton so we have a lot of old tshirts, even really cheap like hand made screen printed ones that say 100% cotton and you can tell it is. They have a little more weight, almost no stretch and and don't have that trademark synthetic fabric 'softness'.

Yet when I try to search it everything I see either says this isn't happen and labels are correct, or it's because its the difference between a weave and knit. I both weave and knit, I know the difference in how the two construction drape and stretch. This is a material difference not construction difference.

It would be one thing if it was only one shirt but it's been every single one in the past year or two.

Has anyone else noticed this? And more importantly does anyone know how we can find for sure 100% cotton or near 100% cotton when the labels themselves can no longer be trusted?