Vintage 70s Royal Blue Ivory White Lace Maxi Dress Tie Empire Waist S or M?

This dress is in good condition with normal signs of wash and wear.

Flaw:  There is a yellow stain on the lace on the front as photographed.

Shown on a Medium (8) dress form.

Measurements of this garment laying flat and unstretched:

Shoulder to shoulder: 14

Underarm to underarm: 17

Waist across: 13.5

Sleeve from shoulder: 22.5 (notice!)

Length (shoulder to hem): 52