risny, I guess you missed the memo, that block of 4 with plate number of C3a is up for auction here: https://www.sothebys.com/en/digital...an?locale=en
and the sale include a non-block of four of a different single. But both of the stamp lots may be out matched in price by the single coin in the auction. The coin went for about $7.5 Million back in 2002.
Perhaps that is why the OP posed the question.