As explained in the post from April 6, the Mumm type 2 cancel was a transition cancel from a year date only format to a year, month and day format. For this cancel the firm simply added an extra line to their existing format. According to the list they only used this format for one date, January 27, 1899. The listing for type 2 is below along with an example of the cancel.
G. H. M. & Co.