How to successfully detect tagging on Canadian stamps?

Phosphorescent...or fluorescent?
Phosphorescent...or fluorescent?

Some of the most frequent questions we receive have to do with tagged stamps. What is tagging? How can I detect tagging? What is the difference between phosphorescent and fluorescent tagged stamps? Winnipeg vs General tags? Many collectors have these stamps but are unable to differentiate them from the regular issues and that can be very frustrating.

 

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