XIX c. Mortise Chisel

XIX c. Mortise Chisel;
Makers mark "Joh. Pet. Müller Söhne" with two marvelous Maltese crosses; I find this mark wonderful. There is a very usefull book, John Walters, German Bladesmiths, an illustrated guide to the brand names, trademarks and monograms found on swords, knives, cutlery, razors and bladed tools, 1871-1945;

http://www.archivingindustry.com/cutlers&toolmakers/cutlermarks-1.pdf

To my great regret, there is not a word neither about Johan Müller, nor about his sons. So, IMHO, either the chisel is made before 1871, or this guy is an Austrian bladesmith.
Any suggestions?