What is the official end of your studies? (The last requirement). The defense, thesis submission...? You are not allowed to work after you have completed your studies, but did you know you have completed them on October 16? This was a concern for us, too, so my wife asked the administration if they could give her a letter on the same day she submitted her thesis. Luckily, it was possible, but they also claimed students never had an issue with PGWP even if notification came a few days later. What does it say on your letter? If it doesn't say October 16 is the last day of your studies, then it might be fine.
In any case, I would explain this in my PGWP application. If it takes time for them to accept the thesis and issue a notice of completion, then there is no way for you to know when exactly was your last day of work. Technically, it should be the date on the letter of completion.
However, also keep in mind that the rules I know mainly refer to on-campus work. I am not sure if there are any differences about working off-campus.