Posted By:
Kevin CummingsI had a bunch of these at one time (all I have left is the Jesse Burkett) and don't recall there being a noticable difference in the quality of the stock on which the cards were printed. I'll compare when I get home later.
The stock issue aside, I don't believe there is any way to distinguish a Koester's card from its E121 counterpart. There are some Yankee and Giant players, however, that are not part of the E121 set, but were in the Koester's set because it was issued to comemorate the 1921 World Series between the two teams.