Hi Renée, although we can't authenticate here, I don't see any reason as to why your label is not authentic - I would expect this to be a '60s dress, although the shape is a little lumpy for a shift. Is it pinned? Perhaps the skivvy underneath is affecting it a little? Are there any other labels (eg, fabric?). Can you tell us a little more about the dress, eg, does it have a centre back metal zipper, lining, what fabric is it?
You're right to be cautious about PC labels though - but this style came back in the '90s so it's good to make sure it's a '60s original rather than the modern inspired style.