Here is a second example contrasting the 1950s compiled list of proprietary printed cancels by Chappell/Joyce with the late 20th century version from the Joyce/Buford collections. The American Medicine Company has two cancels listed by Joyce/Chappell:
Joyce/Chappell cancel list
SEPT. 15 1899.
The Joyce/Buford data has only one additional cancel added: an invert of the December 15 cancel. However, the example above shows there is a stamp undocumented in the J/B list. The stamp above has a period after the month; the September 15 date below has a note that its known copies have no period after the month.
American Medicine Company
New York, NY
Type P 1 CJ Type 1
5/8c SEPT. 15, 1898. Black R No Pd after Month
DEC. 15, 1898. Black R
DEC. 15, 1898. Black R Invert
This is a much simpler contrast that the one for Abbott Alkaloidal. But there are still issues to resolve. There is no substitute for actually handling or seeing the stamps in person to try to resolve the difference between the list at the top of this post, the list at the bottom, and the one example that I have in my possession in between. There is lots of work to do and lots to share.