Was it actually gone or did the remaining stock get some sort of protection? Like did the entire continent seriously get logged?

It got rare enough that by some time in the '90s they stopped even using solid wood for trim and doors in mid-priced houses.

Before the '60s or so, you'd see a lot of narrow-ring old growth flawless, knot-free stuff used in framing and even huge support members, of a quality that'd be reserved for things like solid wood furniture, trim & finishes, and veneer after that (and then phased out of trim and finishes somewhat later).

What happened is it stopped being just as cheap as new growth—that is, it got rare enough and new growth got cheap enough that farming new growth finally became viable, and soon dominated.

Something "funny" related to this happened with wood-shingled housing in the US in the '80s: wood shingles had a reputation for being premium, long-lasting roofing, but this was a reputation built in the era when all of it was thick shake made out of that excellent old growth stuff. It got trendy in the '80s, spiking demand, just as the material for the real stuff, the stuff that was the reason people wanted it, got too rare to practically use for that anymore (except for way higher prices). What was installed was thinner, and made of worse wood.

The roofs installed on new houses in that period soon became notorious for leaks and often ending up covered over with desperately-applied asphalt shingles within 15 years, while the wood roofs were supposed to last closer to 50... but that was the old material, the new stuff was still wood but was not the same product, as that no longer existed as something Mere Mortals could afford.

Almost the entire stock gets logged until there's so little left that they stand up a protection scheme for it. The same happened to teak and rosewood here.