To be fair, 30s gowns can sometimes be tricky in relation to determining which is the front and which is the back, often due to the fact that it was quite common to have a gown dip lower in the back and inset goring that modern wearers might want emphasizing the rear were designed to highlight the hips and so forth. How to avoid such glitches?
- Look for any bust darts. This will tell you which side is meant to face front;
- Look for side closures (in my experience, button/snap/hook/zip plackets typically sit on the left side waist of garments from the 30s);
- Lay the gown flat or put it over a dress form if you have one and see if you see a difference in hem length (often the back hem will dip lower).