Prior art can be submitted under 37 CFR 1.501(a) at any time during the period of enforceability of a patent. The MPEP explicitly states: 37 CFR 1.501(a) permits any person at any time during the period of enforceability of a patent to file a written submission. The period of enforceability typically includes: The entire term of the patent Any period of patent term extension or adjustment The six-year statute of limitations period for bringing an infringement action after the patent expires This extended timeframe allows for the submission of relevant prior art throughout the life of the patent and beyond, ensuring that important information can be considered even after the patent has been granted. To learn more: prior art submission patent enforceability patent term