The dress you absolutely know was made in the seventies might actually be from Urban Outfitters.
The first label ever sewn in clothes was in the mid 1800s.
Style Obviously, the first factor in dating a garment is the style.
My Fashion Eras post gives a brief overview of 20th century styles.
I mean when you’re in a charity or vintage shop, and you find that adorable beaded bias cut dress, how do you know if what you’re holding is 1930s vintage or last weeks Primark? It’s unlikely that they opened Grannies wardrobe and thought, “ooh, lets send all those really old beaded evening gowns to Oxfam”, and if they did it’s likely that shop itself would have recognised it.
If you’re in a reputable vintage store then the hard work has probably been done for you, and you’ll pay accordingly. I rarely find anything older than the 1960s in a Charity Shop, unless it’s marked, and priced, as such.