1923. The 1921 patent date may be for the layout or the instructions. This is a nice house dress pattern. The waist line has dropped but the lines aren't as severe as they'll become in another year or so.
The artist seems to be a bit vague on how to draw a chicken - at least, I think that's what is supposed to be on the platter. If so, that invests the illustration with some additional meaning. "A chicken in every pot" would become part of a campaign slogan for Herbert Hoover in 1928. So in this case we can read the chicken as a mark of prosperity. A prosperous housewife dresses nicely in a housedress she's made from a McCall pattern, and she is able to serve her family a chicken.
McCall patterns at this period offer wonderful details. This is before separate instruction sheets, so they take advantage of the pattern pieces themselves.