That could happen at any time that Satoshi or some other early miner with a large stack of dormant coins decides they wants to spend their coins.
... The fact that they haven't moved since the day they were mined shows that they're excluded from the ones into the actual, realistically assumed circulation.
The fact that they can be moved shows that they will be moved. Bitcoin supply is 21 million and not more than that but also not less than that.