Canada 2009 Internation Year of Astronomy

Not only did Canada Post offer 7500 uncut press sheets featuring their IYA Souvenir Sheets but they also made available 80,000 souvenir sheets with the IYA logo overprinted on it. This overprint was done using UV sensitive ink so you can only see it under UV light. It's hard to see without it but under the right lighting conditions if you look closely in the upper left corner, you can just barely see it. But an easier way to tell if you're looked at an overprinted sheet is to check the product code: the overprints are 6349107202 whereas the non-overprinted sheet is 6349107203 of which 350,000 were produced.