Each individual's CPP amount is calculated as a percentage of a full CPP pension, based on the amounts you contributed and the number of years you worked (contributory period).  

According to canada.ca, your contributory period begins when you reach age 18 and ends when you begin receiving your CPP retirement pension, or at age 70.

My question is this:  if you stop working and contributing at age 65, but defer your pension until age 70, does your contributory period stop, or does it continue to age 70?  

If the contributory period does continue to age 70, then 5 additional zero contributory years will cause your CPP percentage to drop by a substantial amount, particularly if you already dropped the maximum number of low contributory years.