An inventor loses the right to a U.S. patent if the same invention is claimed or could have been claimed in a patent that issued (was granted) anywhere in the world more than one year prior to his/her/their U.S. filing date [35 U.S.C 102(b)]. This usually occurs when a patent issues on a patent application filed by the inventor(s) in a country other than the U.S. over a year before the inventor(s) file in the U.S. It can also occur if someome other than the inventor(s) filed the earlier patent application or (rarely) if the inventor(s) file a subsequent patent application on the invention after a patent has issued on an earlier application. This sort of delay is fatal and results in a "statutory bar" to patentability.
It is important to note that the act (patenting of the invention) can be performed by anyone, and can occur anywhere. It must, however, occur before a specific date. That date is one year before the earliest effective filing date of a provisional or nonprovisional (regular) U.S. patent application or an international (PCT) application that designates the U.S. As far as application of this rule is concerned, it matters not what the date of invention is or that the inventor(s) can claim priority of invention based on the filing date of a non-U.S. (national or regional) patent application. Only the effective U.S. filing date (which can be same as the PCT filing date) is considered.
As the courts have interpreted 35 U.S.C. 102(b), neither does it matter that the invention is not actually claimed in the issued patent used as the reference. All that is required is that "how to make" and "how to use" the invention is adequately described in the issued patent, i.e., that the invention could have been claimed in the patent. It is well-settled law in the U.S. that any invention that is disclosed, but not claimed, in a patent is dedicated to the public.
While this rule may seem harsh, it is well to note that many other countries do not provide any grace period during which a patent application can be filed on an invention that has lost absolute novelty. The one-year grace period is one of the "crown jewels" of the U.S. patent system. It will be interesting to see if that jewel loses some of its luster as global markets for technology grow and the need for patent protection outside the U.S. (in jurisdictions that do not allow a grace period) becomes even more important.