Return to Canada before TN expires?

Does one have to return to Canada on or before the day the TN expires?
I have been working in CA and am driving back next month. Can I "overstay" a few extra days or is that not allowed?

How can you prove that you have returned? As far as I know, the Canadian border doesn't stamp anything in your passport when you cross back. Will they question you if you "overstay" your TN visa? I read about mailing the I-94 form back to the CIS but that wouldn't really indicate the specific date you returned to Canada.

Thanks in advance.

You're supposed to turn in your I-94 when you get to the border. Canadian officials send it on to USCIS.

The generally accepted allowed length of stay after your TN has expired is 10 days.

You have to leave by the time your I-94 expires, that's why they give you one. If you're out-of-status for some reason before it expires (e.g. laid off) you have a "reasonable" amount of time to leave, which CBP generally interprets as ten days.

Obviously you know at the point of entry when your I-94 is going to expire so you have time to plan accordingly.