As an FYI, Ontario used to issue plates every year alternating between white with blue characters (even years), or dark blue with white characters for odd years (e.g. 1965, 67 etc, wrapping with the 1971 issue).

The 1973 issued plates kept getting issued for several years. Dad's late unlamented '74 Chevy was registered in August '74 with the 73-style plates. That is what is still on it in the 1984 photo shown below. I still have the plate from the motorcycle, though I sold the bike the day after the photo was taken.

So, that 1973 plate would technically be correct for YOM plates spanning a few years. They used stickers to validate every year. Ontario has recently phased out the stickers, so I guess one would have to ask at a Service Ontario kiosk regarding YOM plates in those later years after '73.