On my previous post there was some confusion as to the second cover being available now. I have left a comment to clear up the confusion.
However, I have seen Royal Mail issues sold early in the past, but never 3 weeks in advance.
Do you want to make (create) an early pre release cover for the Machin 40th anniversary? If so check out the link below.
By the looks of the picture the seller has a pile 5 inches high.