I had the same query as I face the same issue and hence I decided to call CIC last year.
The CIC agent told me that your work experience which you gained before receiving the PGWP but after graduating from college should be accountable and valid.
I didn't know if I can trust him or not at that time but it seems to be the case.
Here is my case:
Date of first day at work: July 21, 2014
Date of graduation (as listed in Grad certificate): August 2014
PGWP issue date: November 11, 2014
In addition to my study permit valid until November 30, 2014, I had a Co-Op work permit from January 2014 valid until November 30, 2014.
So as you see here, there is more than a 3 months gap between my date of graduation and date of PGWP issuance. (August - November).
Here is the most weird part:
As my first day of joining at work is July 21, 2014 and my pay-stubs were generated since then, I had disclosed that in my Express Entry profile.
Now, technically, I should complete 2 years of Canadian Work Experience on July 21, 2016, right - but what happened is that on June 01, 2016, CIC automatically updated my Express Entry profile and granted me extra 13 points for Work Experience which I deduced to be from increase in 1 year of work exp. (from 1 year to 2 years work exp.)
Also, I received my OINP Nomination on December 09, 2016 without any queries specific to my work experience in 2014 and 2015.
From this experience, I think its safe to assume that we can count our work experience after our graduation. Ensure to check the month of graduation mentioned on your graduation certificate.
Good Luck to all of us!