I agree, my first thoughts are the label looks newer than 70s too, and also think it may be 90s or late 80s.
The Carno factory opened in the 60s, but didn't close until early 2005 - from looking at the labels in the resource, the majority of the the earlier 70s labels just say 'Made in Wales', rather than Carno. Also, the sizing just looks more modern to me, and from the 80s onwards the oval has two circles around it.
I've always thought that 90s dresses don't have where they are made on the same label as the logo - whereas the 80s and earlier dresses have 'Made in X' just below the oval/logo. They're just my observations though. As Ruth says, care labels/symbols may help further.