What dates should I check?
Confirm the patent identity and actual term, then identify the sales, uses, offers, or imports the sender accuses. Section 271(a) limits its specified infringement acts to the patent term. Do not calculate expiration from a single front-page date without reviewing the patent's record.
Can the owner seek damages after expiration?
Section 286 generally bars recovery for infringement occurring more than six years before the complaint or counterclaim. That provision concerns recoverable past acts, not an extension of the patent term. Other damages limitations may also apply, including marking and notice under section 287 where relevant.
What should my response clarify?
Ask the sender to identify the accused period, products, patent claims, and damages theory. Check whether other, unexpired patents are also asserted. Preserve dated product and sales records so the periods can be separated.
Does expiration prove the letter was sent in bad faith?
No such conclusion should be drawn from expiration alone. First determine whether the demand seeks relief for past activity and whether that theory is supported. Describe any verified error precisely.