>>60618797As I said, the law will change so in the future you will have to report any gains in your tax declaration to redeem the first 10k tax-free.
Currently however, as long as you think the 0% applies you don't have to report it.
The bank may ask questions, and depending on how you answer them they will alert the taxman, who will then review your case and decide whether it's 0%, 33% or 50%. This is where you're fucked if you can't document your transaction history. If you've been trading regularly instead of hodling there's very little chance that they'll let you off the hook at 0%.
You can also ask for a ruling in advance of cashing out, but this costs money and has the disadvantage of alerting them to your intentions.