I thought patents expired 20 years from the file date? So you could only troll for ~20 years + anything manufactured using an infringing process. (so "you owe m

I thought patents expired 20 years from the file date? So you could only troll for ~20 years + anything manufactured using an infringing process. (so "you owe me royalties on the widget you made 10 years ago" is valid.)