I happened across this Ladies’ Home Journal cover for February, 1936, and thought it was worth sharing.
This low-backed dress from 1933 has similar fabric flower trim:
Like the magazine cover, this bare backed evening gown was featured in the February, 1933, Ladies’ Home Journal: [CORRECTION: Both are from February 1936.]
The nearly backless gown is made of “a vivid flower print on black silk.”
This low-backed gown was featured in a “Wardrobe for the Young Married Woman,”

Butterick 5321, a low-backed evening gown suitable for the young married woman. Delineator, Oct. 1933. “Slithery, slinky white satin with a deep, deep decolletage in back.”
However, the college girl might also wear a low-backed gown:
They were not just for evening wear:
Low-backed gowns were used to get the reader’s attention in advertisements, too.
This ad is selling hand lotion:

Shelvador refrigerator ad, with a party guest visiting the kitchen in her backless evening gown. July, 1936. Delineator.
This was from a series of ads where elegantly dressed guests visited the kitchen to “ooooh and ahhhhh” over the refrigerator. (To be fair, refrigerators were not that common; on the other hand, this seems like “bad form” — bragging.) The men are in white tie.
Low-backed evening gowns also sold Kellogg’s Bran flakes:
This lovely green [velvet?] dress is selling (green) Palmolive soap:
It’s less surprising that bare-backed ladies in evening dress were also used to sell Fashion classes . . .

An Ad for Woodbury College, Woman’s Home Companion, Dec. 1937. “Earn Good Money as a Costume Designer.”
And pattern catalogs:
Of course, there were also ads for undergarments that would allow you to wear backless evening gowns. This Gossard foundation really does allow the wearer’s back to be bare all the way to the waist: