You should be receiving the form letter in the next couple weeks and that will give you the actual PIR date. If you SRs PIR does end up being Thanksgiving week, it will be a Wednesday PIR not Friday.
I assumed 9 weeks also for PIR, but my son left on Oct. 7th. I received a letter on Oct 11th that his PIR will be Nov 27th day before Thanksgiving. After reading the information in the letter I found that it depends on the day that your son leaves for BC that will determine if they do 7 1/2, 8 1/2 or 91/2 weeks of BC. You should receive a letter with his PIR date listed in the letter.