A patent provides protection for up to twenty years, counting from the filing date (the date given with reference numeral 22 on the front page). US patents with a filing date before June 8, 1995 provide protection for up to seventeen years counting from the date of grant (the date given with reference numeral 45), or 20 years from the filing date, whichever expires later.
However, the patent holder is required to pay maintenance fees to keep his patent valid. In most European countries, these fees are yearly. The USA requires maintenance fees to be paid at 3.5 years, 7.5 years, and 11.5 years after issuance. If the holder does not pay a maintenance fee, the patent becomes abandoned. Many patents are abandoned before the full twenty year term because the cost of the maintenance fees (which increases with the lifetime of the patent) exceeds the patent's value.
Sorry but have to ask is your a post a question or answer? I didn't even know this rule existed. Would have to hope & imagine that NLST's representing firm knows this & made sure management knows. Although they may have already known.
I just looked it up this morning because I had the fear that the companies using NLST IP could just wait it out until they expired. The other thing I didn't know was they have to be renewed at some expense to the holder of the patents. Thought others may want to know. Now will try and figure out when patents were first granted.