I may be lacking some understanding on this matter—can anyone clarify? Let's hypothetically say someone has the ‘luck’ or the means to resolve these puzzles and acquire the BTC. Is this presumed to be legal, and if so, to what extent? Suppose the fortunate individual or team decides to convert it to fiat. How feasible is this, practically speaking? Is selling the BTC to platforms like Coinbase and then transferring to your bank a viable option? I don't think we can realistically expect that BOA, Wells Fargo, etc will overlook a client suddenly receiving hundreds of thousands, or even millions, of dollars... And there’s the potential of platforms like Coinbase restricting high-value transfers. This might work for smaller amounts, but some of these addresses are worth hundreds of thousands of dollars each.

Returning to the legal bit, how does one justify these funds? Informing the IRS that it was a giveaway from a random forum user is bound to raise eyebrows, right?

I'm not intending to discourage anyone; I'm genuinely curious about how such a substantial BTC to fiat exchange would occur without legal repercussions...