525pi/pii , 6c Christmas, center of block of 4, W2 Unlisted Tagging Error. Stamps are tagged at each side instead of through the middle. C/V $300 ($200 + 50% for block without the scratch through window vatiety), without considering the error. Also, this block is "surrounded" with other stamps from the sheet.
This is a very nice, VF addition to any collection!