The latest patent date on the envelope is 1925. Remember that patent dates on patterns frequently refer to the pattern layout illustrations or construction guides, not the styles themselves. There is a wonderful article about this topic here.
Costume, masquerade, and fancy dress are all terms used to describe this type of pattern. The description for this one reads:
BOYS' MASQUERADE COSTUME. This Brownie costume consists of a suit, short open-in-front jacket, and pointed hat. The suit is sleeveless and closes at back. Bands finish the edges of the jacket which has long one-piece sleeves.
Palmer Cox is the father of the Brownie figure as we now know it. The first book of Brownies stories, The Brownies, Their Book, was published in 1887. Cox followed this up with 15 more books about the Brownies. Cox died in July 1924 and in an obituary in the Carbondale (Illinois) Daily Free Press, among his works is listed The Brownies in Fairyland, a "cantata for children." Cox was a Mason and the Grand Lodge of British Columbia and Yukon provides some very nice information on Cox, and where the publication date of The Brownies in Fairy Land (with music and Lyrics by Malcolm Douglas) is listed as 1925.
One can imagine The Brownies in Fairyland being performed at school and summer camp pageants, so it's quite possible that Pictorial Review saw this pattern as an opportunity to cash in on the need to dress dozens of squirmy children in Brownie suits.
This is another one of Pictorial Review's wonderful printed patterns. The tissue instruction sheet recommends stuffing a pillow in the front of the suit and tissue paper into the toes of the boots. Now and again a sewing pattern presents a little archaeological evidence. In this case, an extra or unused facing was tucked in among the pattern pieces.