Excuse me, I didn't quite understand what you meant. I've accumulated this sum of bitcoin through a variety of sources. I haven't bought a single one. Theoretically, isn't this income something that should be declared? I'm talking about the whole amount of coins.
What I meant is that it's only you who knows where you've got those coins from and whether it's by working for them, or mined, or you've bought them long ago when KYC was not everywhere. And I don't think that anybody would invest too much of resources to find out if your declaration is for real or it's hiding a bit of details here and there.
Hence if you declare them as income then you'll probably pay income tax and if you declare them as capital gains (from 0 since you don't have receipts), then you'll pay capital gains tax.
That's how I see the things.