No, they weren’t. The mint stolen coins were $30K of ALL $20. This included other denominations, and mint marks.
Furthermore: What did their real estate purchase agreement state? Did they buy the entire property, with free and clear title to everything contained therein? Second, how can the state prove that those coins must certainly have been the stolen ones? Could no one else have amassed a fortune that large, and hidden it? Seems the state would have to prove by some physical evidence that certainly connects those coins to the heist. But there were millionaires even back then, and $27,000 would have been but a fraction of such a person’s wealth.