Statute of limitations
From Conservapedia
Statute of limitations is a law that sets the time within which parties must take action to enforce their rights.
Most jurisdictions have a general statute, as well as more specific ones. For example, under the United States Code, a government contractor (as well as the government) both have six years from when a matter was known or should have been known to file suit against the other party.
In most cases, the amount of damages does not have to be known specifically.