I, personally have catalogued about 25 of the 1920 Type 1's and about 35 of the 1921 Type 2's--there are likely at least 80 in each set, and I have seen quite a few Holsum' that were not accompanied by a back scan so I couldn't include them in my research.
Type 1's have been dated to 1920 (at the earliest) by the following 2 players that began their careers for that team in 1920 (the Strunk w/ arms at side is a Type 1, the batting is a Type 2)...
The Type 2's have been dated at 1921 because I have seen cards of both Eppa Rixey (Cincinnati) and Walter Schang (New York Yankees), both of whom began their careers with those teams in 1921.
Type 1's are those that have the "H." from "H. Weil Baking" all the way to the left border on back, the Type 2's have the "H." indented slightly. Small difference on back but a big difference in the subjects of each set.
-Rhett