It is my understanding that once a patent expires there can be no claims made for infringement thereafter. For there to be a valid claim, I believe, the infringer has to be notified while the patent is in force.

The Statute of Limitations of 6 years is retrospective in that infringement damages can only be claimed for the preceding 6 years, from date of notification, even if the infringer has been infringing for 12 years, for example.

35 USC 286 and 35 USC 271(d)(3)

Corrections more than welcome.

.

.

Be well