Norinco is a Chinese company, right?
There are different degrees of patent or copyright infringement enforcement depending on the country. There are many Chinese companies that blatantly copy designs from other countries without reproach.
Anyway once the patents are expired, then it is public domain. Nobody is "copying" it at that point, they are simply using what is known as "common knowledge" to those "skilled in the art" of firearms design.
Furthermore there are two types of patents: design patents and utility patents. The design patent, while you might think applies to some mechanical or functional design, actually applies to what would normally be called the "look and feel" or "shape", it is sort of like a copyright for physical objects. A utility patent is where the real action is, and they have to provide exactly what is novel or new about a particular method or apparatus such as a pistol. One would think that there is little legitimate, patentable innovation in firearms design.
Glock certainly does not have an enforceable utility patent that would have been in force during their first generation pistol production, since it has been over 20 years. But it is routine for companies to revise a design and file a new patent that is only different in a small way to the original patent, thus extending the protected period for a design. I have no idea what Glock has done in this area but it would be interesting to read any Glock patents and see how they were written.
AFAIK the S&W v. Glock lawsuit resulted in a very, very minor change to the Sigma sear assembly, and I tend to agree with S&W that the suit had virtually no merit, even if judging only by the fact that S&W made the change with zero impact to the function of the pistol.
