That works until it does not. What if you transferred the BTC to other wallets or exchanges in the meanwhile? Even if you still had access to the original wallet, what proves that it was really yours? etc.
If you and your friends are just innocently idling in a your car wearing a ski mask in the middle of summer with a shotgun and a large duffel bag, in front of a bank that was robbed in this manner four times last month, you're highly unlikely to, at minimum, beat the ride.
Or is this just a theoretical concern for anyone who isn't laundering Bitcoin stolen through ransomware or from exchanges?
Did the jury have reasonable grounds for voting to convict?
And some of those interactions are taxable events - e.g. if you are exchanging out of cryptocurrency denominations, then by US tax law as a US citizen that was a taxable event.
The issue of provenance is an issue regardless of the type of funds.
In most jurisdictions the burden of proof is civil, so more likely than not.
The original claim is easy to prove: it'll be in a wallet which was held for that amount of time. The bank isn't obligated, unless you turn up covered in blood, to prove that you didn't just beat a guy with a hammer till he gives you the password - because you'll go down for that crime by other means.
But very few people engaging in ongoing criminal transactions are going to have a supply of aged BTC accounts to use in trade for goods and resources, and certainly you'll trigger red flags if you keep turning up with a brand new "held it for years" account of $50,000 each week. I mean we know this: because it makes headlines when untouched BTC accounts start moving.
Simply swap into monero and then send it to anybody else.. Maybe lets say you have 100$ in btc, you convert it to 100$ in monero and just spend 10$ 10 times in a span of a week and I am sure that nobody can keep track of it.