The mystery:

Why are so many of these perfins mint?

Ginn & Co. used perforators at their offices in New York and in Cambridge, Massachusetts. These offices perforated a very small number of Canadian stamps, some of which are shown here. The top row is from the New York office; the bottom row is from the Cambridge office.

The top stamps are from the same sheet; this pair was discovered in Canada. They were the only perfins in a large collection of Canadian stamps. Both are mint.

The bottom row has stamps from a variety of collections. All of the 1¢ Medallions are mint, as are the other nine stamps of this issue I am aware of. The 2¢ Queen Elizabeth is used, as is the other stamp of this issue I am aware of.

The solution:

Unsolved!