Excepting a few experimental K actions, all commercial Mauser actions, short, intermediate, standard or magnum length, round or square bridge, had thumb cuts and clip slots until the 1930s.As justcurious writes, the thumb cut was protected by Mauser as a means to gas escape in case of a blown primer or ruptured case. This was not so rare a occurence in the 1890. The Mauser action blows gas that has entered the bolt into the left side of the receiver, from where it it can escape through the generous opening of the "thumb cut" without doing harm. Gas that continues to the rear past the "thumb cut" is then taken care of by the gas flange on the bolt sleeve.