Hi and welcome to the forums. If you haven't gotten the chance hit up your local bookstore and pickup a copy of the Charlton Catalog for Canadian Government Paper Money. Inside there is a very detailed guideline on the way notes are graded.
From experience your UNC62 is probably because your notes had cutting cups (on the bottom of the note where the security thread is this usually is the difference between Gem Unc and Choice Unc). Of course minor flicks, damage/bending from currency bands and many other things could have contributed to degrade the note from High Unc to lower unc.
