To summarize: Most American closed-car designs in the period approximately 1934-1940 were awkward. In part, this was because body and production engineering could not evolve rapidly enough to deliver sleek streamline-influenced designs stylists were capable of dreaming up. For the 1940 model year, General Motors finally produced attractive closed cars in the form of its redesigned C platform. But while these cars were attractive abaft of the front axle line, their front end styling seemed a little more dated.
This changed when GMs C body lines were facelifted for 1941. An important factor was integration of headlights into front fenders, something GM was slow to do apparently because Engineering had objections. The other improvement component was grille design. Grilles for 1941 (with one possible exception) were much better matched to the rest of the styling.
Below are comparative images of 1940 and 1941 frontal designs. Missing is a comparison for 1940 LaSalles because that brand was dropped at the end of the 1940 model year.