Great information. Yes, sadly, the print alone does not guarantee authenticity and associate it with a particular designer.
I worked for a fashion designer in '93 who would have custom-made fabrics woven and printed in Italy, so you would think there was a guarantee the dress was his if the fabric was, but every season he had factory sales to sell off the left over fabric and anyone could buy a piece and make it up into anything they wanted.
So Debbie W, considering that your dress has no labels, I recommend looking at the construction to see if it's of home or professional standard, and consistent with '71 techniques. The style could be '71 but it's very plain - does it have a centre back nylon zipper? Are the openings faced? How are the seams and hem sewn? Does it have a lining? Etc.
If you're not of the answer, post pics of these areas and we can help.