From the book:

The late 1930’s and early 1940’s are the eras that this sweater hales from; the neat collar, keyhole neckline, and slightly puffed sleeves are all hallmarks of that time. We have made the sleeves longer than the original, so that the sweater is more versatile - and because we can afford to be a bit more extravagant with yarn than in those times of austerity. The openwork panels on the front and shoulders give textural interest, which also emphasizes the neckline, all features of the vintage look.