Whether this placket front opening was real or just a feature of the design is not relevant.
The contrasting material with its contrasting buttons makes the placket distinctive.
This design feature of almost belongs in the later bib feature group. Extending as it does from neck to waist makes me consider it a style of its own.

Date about 1931: Age about 20 years old  • Estimate: born 1911 ± 3 years