You're right, they aren't , and they run for 20 years apparently? So if the patent was enforced, and it was made by HW, or the glasswork he was at during the patents lifetime, this would bring us to 1925 since he patented the technique in 1905. This would mean it could still fall under Thomas Webbs or the Stourbridge Glass co. as that was where he was during the patent.
It also means in 1925 or 1926 ( assuming the patent had been enforced ie. no one else was allowed to use it during it's lifetime), that other companies could have started using this technique openly.
Two comments about this -
IN 20th Century British Glass Charles Hajdamach comments that Mrs Graydon Stannus had access to glassmaking facilities from 1922 and that Graystan closed in 1936.
IN British Glass 1800-1914 Charles Hajdamach makes a comment page 278, on discussing HW patent for this particular technique - 'In 1905 H Wilkinson of 10 Dennis Street, Amblecote, adjacent to the back entrance of Thomas Webb glassworks, patented a technique using threaded glass which must have been known to 19th century glassmakers and which is sometimes used by studio glass makers.'
I infer from that last comment, that pieces must have been seen, which had been made using this technique, dating to the 19th century and also from studio glass makers at the time the book was written. Would that inference be correct?