Unfortunately no. Even though the rest of the address is identical, that at the time of sending your application it was CPC-PGP, that you likely received a signature to confirm receipt via Canada Post, this is a fatal error. Your parents application will now be rejected.Its funny how in the reminder emails CIC added an additional "M" to the address where application needs to be sent.
CPC-M-PGP
PO BOX 8020, STN T CSC Ottawa, ON
K1G 3H6
v/s
CPC-PGP
PO Box 8020 STN T CSC OTTAWA ON
K1G 3H6
Now, I did submit my application after I got the reminder email but I still posted it to CPC-PGP.
I hope that would still be okay?
End sarcasm.
Of course it's completely fine. It's great that we have a community here that is always on the ball and picks up even these small details, but we really need to relax a little sometimes.