There isn’t much information here as I have observed very few factory differences in the shirts.
The striped shirts from the Windbreaker Outfit (#10) appear to come in two fabrics.
Version 1: A thin cotton t-shirt material. Known factories: OK
Version 2: A thicker synthetic material. Known factories: P, PMI, LF, IJ, WW
In general, Version 2 tends to be larger (physically) than Version 1.
I don’t know much about the shirts that come with the foreign outfits except for Jesmar outfits.
Jesmar shirts are sometimes solidly coloured but are generally striped. However, the colours are not always ways and [insert colour here]. I also have one shirt recorded that’s white with small polka dots. They are often a very thin fabric, are badly sewn with very thin hems, and have unfinished bottom hems. Some also have typical Jesmar Velcro.
The shirt for the 25th Anniversary Windbreaker outfit likely doesn’t have a tag in it. It will be purple and white. However, I can’t confirm this as I’ve never actually seen it myself. This is the only girl’s 25th Anniversary outfit I don’t own.
The shirt for outfit #100 is blue and white striped and the most obvious difference from outfit #10 shirt is the red CPK logo on the chest.