Canada Post has announced that the Canadian Year of Astronomy hidden overprint of the IYA logo souvenir sheet is sold out and no longer available. The overprint can only be seen using an ultraviolet light, although if you tip the sheet under natural light you can tell 'something' is on the top of the sheet. You just cannot identify what it is without putting it under a UV light.
These sheets were issued on April 2, 2009 and sold out almost immediately.
There were only 80,000 of these overprinted sheets printed vs 250,000 of the regular souvenir sheet without the overprint.
Good luck searching for this sheet.
(From posting on Stamporama)
