Ah thanks, they are diamantes or glass faceted stones, not sequins, and prong-set (rather than glued/sewn on) which is usually an indicator of some age. I think you're in the right area with 20's. I'm not familiar enough with the older clothing to narrow the dating I'll leave that to somebody else, I just wanted the closeups to confirm it wasn't a 80's/90's lookalike. (I see so many of these, usually in black or navy that are far more modern!)
Btw, is it a dress or a two piece top & skirt?