I've posted on the other forum regarding this 501 issue and would pass comment on the auction itself.
One interesting side-show: if there are only 500 STuGs and the certificates were numbered to 507 then it's likely that the first proper certificate is actually 2 instead of 1, and that at further regular points there'll be a missing number.
I'm guessing that from the possibility that the first page of a book is never numbered from the left-hand side of the opening gatefold, always on the right. Similarly decks of cards evolved with jokers and other test plates.
I'm farily sure that there's a rare rectangular piece of card with the number 1 and so forth in the sequence, up until the point the guillotined card sequence is initiated (eg it could be 1, 75, 150, 225, 300, 375, 425, 500 or perhaps a run of copyright/test cards of 1 to 7 after which the 7-507 certs printed). Because it is likely that the printers were Chinese it is always a possibility that they set the sequence to print 500 of the completed certificates, leaving this intermittent loss at the various stages.
I'm farily ignorant of the printing process and could be wrong but I'd think it more interesting challenge to try to put together a registry of all 500 certs. Obviously people could remain anonymous but could put a unique identification of some sort beside each number, and we'd eventually find out which numbered certificates do not actually exist.
What would also be interesting is the possibility that Andy would then need to distribute these retained certificates to those who didn't obtain any because their numbers were lost in the printing process: it is conceivable if there are only 500 certs, of which some happen to be over the number 500.
Any thoughts?