I’m sorry that these two dresses are not on exhibit now; they really opened my eyes when I saw them several years ago, side by side like this, and I would love to know more.
They surprised me because, although I knew that couturiers make adjustments for private clients, this seems to be an illuminating example of how much a designer is willing to tinker with a design to suit individual customers. It’s possible that one of these gowns with the Lanvin label was altered at a later date [the Met doesn’t say], but the difference in the sleeves, for example, seems to be original to me. The Met hasn’t supplied much information, but click here to see the image at a larger size, and here to see the label.
For a long time, most of the women who could afford couture were “women of a certain age,” so it’s not surprising that, for example, a dress shown on the runway with a completely see-through bodice — or open to the waist — may have a layer of concealing, flesh colored lining added for private clients.What I love about these two dresses is the way that one has been modified for a smaller, and possibly younger, client.
The sheer fabric in the neckline (cut lower and gathered, on the left dress), the length of the bodice, and the shape and decoration of the sleeves, are all adjusted to flatter two different clients. Because the dress on the left is for a shorter woman, the appliqued trim has been carefully rescaled to fit. (Imagine the dress on the right, cut at same the waist length as the left one. The waist seam would be almost touching the trim. Because they aren’t perfectly side by side, it’s hard to be sure, but the dress on the right curves in at the natural waist and then curves out toward the hip.) The dress on the left seems to be made for a more girlish body.
Look at the trim on the skirts. This is not a case of simply shortening the black part around the hem. The scale has been adjusted; where the bodice is shorter, the light colored part of the skirt is longer, to compensate, and the whole dress remains beautifully proportioned.
Lanvin’s “robes de style” — with these dropped, but semi-fitted waists and full skirts, unlike most 1920’s couture — were often aimed at a younger client or a debutante.

Lillian Gish in a Robe de Style [designer not named]; Delineator magazine, Spring of 1925. Photographed by Kenneth Alexander.
“The immemorial symbol of growing up is to put up your hair. So the debutante is letting her hair grow to her shoulders, waving it softly and dressing it in a tiny roll at the nape of the neck.”
Click to see an earlier example of a “Robe de Style” by Lanvin, 1922. Although this fashion could be worn by women who were long past their debuts, Butterick aimed its full-skirted 1920’s patterns at young women and teens.

“For the young girl Paris suggests . . . .” Fashion report, Butterick’s Delineator magazine, Feb. 1924.
This dress (below), which has floral trim and a contrast hem like the Lanvin gowns, comes from a Paris design house called “orange.”

Center: a Paris gown suitable for the “fille d’honneur” at a wedding, designed by “orange.” Delineator, Feb. 1925.
“A frock that would be altogether charming for the “fille d’honnneur” of a wedding-procession begins and ends with a yoke and band of green chiffon. The frock itself is of white mousseline de soie garlanded with pink and green embroidered roses and leaves. From orange.”
Butterick offered these patterns — probably influenced by Lanvin — for Misses aged 15 to 20 in January, 1925.

Party dresses for Misses (age 15 to 20), Butterick patterns Nos. 5755, 5714, 5743. Delineator, Jan. 1925.
However, this “robe de style” — designed by Jeanne Lanvin — for 1926 is definitely sophisticated:
I wonder if some clients asked for the “nude” triangle filling in the very low bodice to be higher — or lower, or not there at all.