Namely, Theodore I, Marquess of Montferrat wrote what is probably the last Roman(Byzantine) military manual ever(Les Enseignemens ou Ordenances pour un Siegneur qui a Guerres et Grans Gouvernemens a Faire) and it was written first in Greek and then translated to French by Jean de Vignay.
I need access to that work in English, is there anyone who could point me in the direction of it?
It appears that the English language scholarship on this references only the French. This page has a small bibliography with some English language works on the topic, but they may too only reference the Knowles version at best. I'm not sure anyone has bothered to translate it from the French, but maybe a byzantist may have a flash of inspiration?