My guess is that valuable items have appeared in Canadian attics in the last 48 years that are not mentioned here. This was probably a pretty good guide in the 1960s and 1970s. Maybe even the 1980s. It’s too old to claim “almost every conceivable” anything now, though. There were items created after 1963 that can now be considered valuable. Maybe not antique, by its official definition (100 years makes something antique), but definitely “art objects” worth knowing about if you are a collector.
Here’s an interesting item that can be found in a Canadian attic: