Indeed.

What UK off-the-peg brand(s) (made in Romania?) have single needle side and sleeve seams? Are not most double needle? I may be mistaken, but I think BB uses single needle sewing on its side and sleeve seams. Even Hilditch & Key at one time used double needle sewing on its arm seam. No quality US maker uses double needle arm seams on dress shirts.

Better quality US RTW shirts have been using the questionable split yoke for years.

Sea Island 140s cotton was an option in most better US made RTW shirts 20 years ago. Behar, The shirt co. that became Talbot shirts, Troy, Polo (although most were made in England), Eagle, Gitman, Individualized, Kenneth Gordon, etc. Nothing new about Sea Island cotton in US made RTW, although back then it was questionably labelled by the Sea Island trademark owner, Threadtex of Japan.

Some Brit label shirts use fake split yokes that are just seams, not separate pieces. A well known US shirtmaker has also been guilty of the subterfuge. Held to a light, the light will reveal about 1/4" internal cloth inlay on each side of the seam in a real split yoke.  If there is no cloth "shadow" on each side of the seam it is only a seamed yoke, not separate pieces sewn together.

They failed to mention that better US RTW shirts have a separately constructed and sewn-on front placket. More expensive to produce than the typical UK placket which is folded and sewn as a continuation of the shirt front material.