These upside down backs are extremely rare.....on the order of broadleaf 460 rare.....they occured when printer inverted the sheet the wrong way.....
they are out there, but very tuf to aquire.....if you see one , get it....if u can afford it ....they don't come up too often......most i have seen are factory cut.....and most are piedys or sweet caps(probabilities finding sweet cap and piedy are greater since they are the most common backs)....
.....took me over 14 years to aquire a few, and boy i'm glad i snatched mine up when i did