In this home sewing tip from the wonderful Ruth Wyeth Spears and the 1920s, the collarless V-neckline was evidently a new and very smart style! She explains in careful detail how to finish the V-neckline with a bias facing, rather than a bias binding, for a more chic effect.
When working with patterns from the 1940s and earlier, facings were,
well, simply not included as pattern pieces. It was left to the seamstress to know how to face a seam. The
seamstress could use bias strips (as described in this article by Ruth Wyeth Spears), a bias binding, or simply cut a piece to match the outside shape of the piece
to provide a neat finish, using the same pattern piece or pieces being faced as
the template for the facing. Facings are typically made of the
same fabric as the
garment, but may also be made of lighter-weight fabric or in a contrast color.