Ingots like these are not forgotten by those who buried it. They retrieved it looong ago.
.........................................
Unless they died before they got the chance!
In a haul this large there would be more than one person. And people talk.
I do remember a case where a guy stole gold or silver bullion from the San Francisco mint around the 1900s(IIRC)and he buried a lot of the coins. He died and the coins were later found by accident.