I know the question was not addressed to me, but in my experience, such agreements do not actually "expire". They can go on forever. Meanwhile, the land/claim holder is free to also "explore" other possible agreements, meaning multiple non-disclosure agreements can exist on the same ground. One usually only finds out who the interested party/parties may have been if an greement is reached, not to include the party/parties left out.
...all in my experience and opinion.
VP in AZ