That could also be a matter of timing or as you suggest, of rivalries. It’s kind of surprising how much these people knew given the limitations of their period – no phone, no radio, no internet, and travel only by horseback. Books copied by hand. And yet many of these fechtbüch authors do seem to either know a lot about or actually have copies of many of the other books, which is pretty amazing. It’s not like just downloading from a link today!
But they may not have all known about all the other contemporaneous authors. We do find some gaps like that. I’ll ask my friend Christian Trosclair who does a lot of the translations on the Wiktenauer to chime in here if he has the time, he can probably provide some insight.