I just looked at the provenance section (again) and I don’t see any proof regarding when the coins actually left the Mint. If it were known when that occurred, presumably, there would have been a report of missing coins at that time. That is, unless there had been an exchange, for which there is no record. Additionally, I seriously doubt that the cashier would wait approximately four years after he first had access to the coins, to steal them, exchange them or otherwise get them into the hands of Switt.
For the record, I don’t care about “rare gold” any more than I do rare cooper or silver.