The distinction that trips owners up is between a reassessment year, when values are updated across the city on the province's multi-year cycle, and an ordinary year, when a notice can still be issued for a correction but the surrounding evidence looks different. Both carry their own printed deadline regardless.
There is no appeal path once that printed date passes for the year, which is different from some other tax matters that allow a later correction. The Board of Revision works strictly from the deadline on file.
Check the notice in hand rather than relying on what last year's deadline happened to be. Get your hand-reviewed valuation from Joel Dyck.