NYC-YYZ yesterday. only 3 seats available on the 10:20. Book rest of my family on the 10:20 and myself on the 9 AM. Showed up to the airport a few minutes after 9 (we were checking luggage-gotta love flying business, we checked 7 bags, some of them 70 lbs). Kiosk didn't pull up my reservation as the flight had already departed (if I had been a few minutes earlier the kiosk would have been able to put me on the next flight...). Went to the check in desk. Put me standby on the 10:20 no questions asked. No seats in business so I sat in economy.
Lesson learned: if you don't have enough seats on the flight you need just book the previous flight. No need to lie and invoke the "flat tire rule."