The California couple uncovered eight cans filled with more than 1,400 coins on their property, in what is believed to be the most valuable treasure trove ever discovered in the United States.
They took them to a firm specializing in ancient coins, Kagin's Inc, which valued them and announced last week that they will sell them, via online retail giant Amazon.
But on Monday the San Francisco Chronicle linked the find -- called the Saddle Ridge Treasure trove -- to a robbery at the San Francisco Mint.
If proven to be from the US Mint, the coins might be the property of the government and have to be handed back, according to an ABC news online report.
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Kagin Inc boss Donald Kagin however told AFP he was "very confident" that the Saddle Ridge trove was not linked to the San Francisco Mint theft.
"There's a number of reasons why they can't possibly be" connected, he said.
In addition the stolen coins "would have all been mint state, recently struck coins," he said.
"But only some of the coins in the Saddle Ridge horde are. Many others are circulated coins, struck over a long period of time and clearly buried over a long period of time.
"The only parallel here is the similar (face) value. But again, not even that's that close because of the different denominations," he said.
Kagin said plans to sell the Saddle Ridge hoard in about two months remain in place.
Asked if he could guarantee to the couple, named only as John and Mary, that there would be no hitches in the sale, he said "Nobody can guarantee anything".