You asked how one could tell?
By 30 years of studying and experience.
based on 300,000 photos taken in the best museums and their reserve collections, plus a private library comprising 3,000 books and catalogs.
There also were Katzbalgers with single edged blades, as well as Katzbalger sabers, especially in the later period of that type of Landsknecht swords, so your blade is not unusual at all.
Best,
Michael