I'm talking about all jewellery - antique, 70s, 80s, now.
A heavily stylised 70s piece, might not appeal to everyone now, but a classic cut won't even indicate the decade it was made from the style alone. Are you suggesting that classic cut 80s platinum & diamond jewellery wouldn't be popular now?
My mum was married in '68, she has a platinum marquise cut diamond engagement ring. It's a classic that would be difficult to date.
Bags only retain their value if they're in mint condition, and a bag used for work won't keep its condition.