I've got a bunch of old TLD D2s but had more, most of which annoyingly got binned by my dad years ago when I was storing them at his. And yes, I'm still salty about it as he asked what I was going to do with them. Save them I said, I'll grab them next time I'm over. Bin them he did, without asking, including two custom painted ones. He'll have a shed so full of empty cardboard boxes that you can't get to anything yet will throw out stuff that's actually meant to be kept, probably so he can use the space created for more F'ing cardboard.
Still got my original '95ish Specialized Mountain Man helmet though, even if it doesn't fit me anymore. I have contemplated airbrushing one of my TLD open face lids to replicate it though which I think would look quite cool.
Personally I wouldn't use an old helmet, they're purely for display. If the foam is not used and kept out of UV then an unused helmet could probably still be safely used but if it's seen any use in the outside world or exposed to chemicals, sweat and UV it's just not worth the risk. A few years ago I ended up buying a new TLD D4 to replace my old, original D3 that was from 2010. That had only seen a few years use, but it was still nearly fifteen years old which for PPE is a big stretch even if a lot of the inherent strength in it comes from the carbon shell rather than a polycarbonate one.