"Your medical exam results are valid for 12 months only. If you do not come to Canada as a permanent resident within that time, you may need to have another exam."
From what I understood, in addition to entering/landing in Canada before the expiry of the PR visa (as indicated in the COPR, which is your point that I totally agree with), you must come to Canada as a PR within the time your Medical Exam is valid or else, you might need to have another medical exam.