I think it was me that bought the coin with the '1'! It's probably rarer than the dateless coin, but that could be due to the fact that the dateless one is easy for the layperson to see. There may well be the same amount of '1' coins out there, but no one is looking for them. And, even if they were looking for them, a die number (if that's what it is) is much less spectacular than a mule. Did I not read something somewhere to the effect that the RM also acknowledged the 'number 1' 20p at about the same time as they acknowledged the dateless mule?? I'd be relunctant to send it off though. Did you send them high re pictures of it? As for the metal mix or finishing of the blanks, instinct tells me that a bad mix etc leading to an odd tone wouldn't really stir up much extra interest. Even with a letter from the mint, it's just a slight flaw leading to a differently toned coin. Worth a couple of quid as an oddity perhaps.