On the CIC website I read (cant remember exactly where) that the PCC are usually valid for 12 months. I then read about an EE applicant that submitted PCC older than 6 months and their application was declined because of this and they had to re-submit the entire application.
So, I am not 100% sure how long they are valid.
I then sent an e-mail beginning March to my local Visa Office and asked them about this. I asked if the attached documents would be sufficient and pointed out that two of them passed the 6 month date and one will be 6 moths old later this month. I received a reply last week that I should submit the original PCC (they did not tell me if I can courier/post/drop off in person). They said in the e-mail that they will request new PCC if it is required.
I have already applied for new PCC in March and have already received them. I am traveling to the VO today to hand them in, in person, and hopefully to find out how far my application is and if there is anything else I can do to speed it up.
As long as your application is received by CIC before the expiry date of the certificate it will be fine. Make sure that you send the application with UPS Courier Services www.ups.com as they have a branch in Sydney, Nova Scotia, this way you can track your package online and receive a waybill online that shows the exact date they received your application as well as the person who received it. It might be a little more expensive, but this is worth the money and it will give you surety that everything is order with your application.
Hit the [good] button if this helped
