That's my understanding, yes. There was so much old-growth wood (in North America, anyway) that practically all lumber produced was excellent by modern standard

That's my understanding, yes. There was so much old-growth wood (in North America, anyway) that practically all lumber produced was excellent by modern standards. No reason to bother with young or otherwise low-quality trees. I notice that working-class houses of the 60s-80s (and a bit into the 90s) usually had solid wood trim and doors, too, typically throughout. Those are now luxury-tier, and even rather expensive houses will use particle board (basically cardboard—sawdust and glue) or pieced-together pine that must be finished with paint, and hollow doors, often without even finish-grade veneer (so they have to be painted, can't stain and varnish them). Expensive houses where the person building it cared a little more (or the buyer had input) may put solid wood in certain public areas, but e.g. bedrooms? Hardly ever, now, at least in houses built for/by people who work for a living. So the process of lumber-worsening may be ongoing.