Canada
can-20180518-z-003
page = 1
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Width: 183 mm
Height: 134 mm
Location: Ice Hockey Volume XXXV
Stamp ID = 6138
The envelope that contained Canada Post's invitation to the stamp unveiling for can-20180518-s-001. The envelope also has one of the "Personal Postage" stamps printed exclusively for mailing the invitaions, can-20180518-r1-001.
From Linn's "Stamp Issuing Entities Of The World" page
Canada (1851-)
Stamp-issuing status: active; Population: 29,123,194. An independent state within the British Commonwealth, occupying the northern part of North America.Courtesy of Kon Sokolyk.