You aren't calculating patent terms correctly. For patents filed before June 8, 1995, the patent is valid for the longer of 20 years from filing or 17 years fro

You aren't calculating patent terms correctly. For patents filed before June 8, 1995, the patent is valid for the longer of 20 years from filing or 17 years from granting. Patents filed after June 8, 1995, it's 20 years from filing dating. All of this is shortened if the patent claims priority to an earlier patent. And it's possible to get an extension under § 156 of the Patent Act. The USPTO has a calculator but you have to know quite a bit about patents to effectively use it. https://www.uspto.gov/patent/laws-and-regulations/patent-term-calculator https://www.uspto.gov/patent/laws-and-regulations/patent-ter...