I am familiar with the type of darts and the silhouette. The 80s 'nodded' to many eras and appropriated them. So the combo I see here, as well as the fabric and its colors point to 1980s.
Why the seam technique... in the 80s... first, there have been surged seams for long long time now. You may see them on commercially produced menswear in the Edwardian era. A home sewers would used a few techniques to finish a seam - from French seams to a quick zig zag along the edge. There were pinked seams too. Which the home sewer might choose depending on, my theory, skill level. I have seen gorgeous French seams on seamstress made gowns but my grandmother used them on most everything because that's how she learned in the 1930s.
If I were going to pick an end of the 80s for this... mid to around 1988... that collar was really popular then. Think Donna Karan.
But you seem dead set on this being 40s. lol