Recently I've published two posts about the William Blenkinsop Penny Black Cover that went to auction at Sotheby's (February 2024).
In the first post titled Could this Penny Black become the most expensive British stamp ever sold?, which I published prior to the auction, I wrote: "Should this earliest known example of Penny Black postally used sell anywhere near the £1.17 million lower estimate..."
I took 'earliest' from the literature on the Sotheby's website. Quote: "this remarkable survivor is recognized as the very first postage stamp delivered in Great Britain"
It has been pointed to me out on reddit that this is incorrect. And I agree. And so it seems a host of experts would as well.
Because back in February 1999, in Switzerland, a Penny Black Cover dated 1st May 1840 went to auction. With expert certificates from Peter Holcombe, Michael Hall, British Philatelic Association Expertising and The Royal Philatelic Society, this is surely genuine. To me it's as genuine as genuine could be!
The First Cover, May 1 1840 is a pdf article that is worth a read on the David Feldman International Auctioneers website. It gives a good deal of information about the first cover, the provenance and how it has been expertised multiple times.
So it's likely this is one of the reasons the William Blenkinsop Cover failed to sell.