And just to clarify my reasoning. The aforementioned images in Breu's sketchbook are perfectly mirrored to the images in C93, as can be seen in the composite image below.
Mirrored images occur every now and then especially in prints, not seldom as copies of artwork is made by other artists. Images that quickly come to mind are also attached and are made after originals by Jost Amman. It would seem likely that this could also happen the other way around, with preliminary sketches being mirrored versions of planned engraved plates.
This could indicate that at least the images were at one stage suggested to be engraved rather than painted. I have always found it a bit odd that a man who clearly felt that the fighting arts and social status were both very important chose to create manuscripts with single copies rather than printed volumes that could be sold in more copies. A unique book of course offered a unique value even then, if you had the right client...
This image shows a version of a Breu sketch that I have reversed to what I believe was intended. The first is from the Breu Sketchbook, the second from C93 and the third from 393, just for reference. Only the Breu image has been reversed by me.
Interesting to note in the Breu image, is that the dussacken might actually be made out of steel, which could reinforce the theory that the dussacken were wasters for the 16th cent. sabres.
These two images are reversed copies of printed Amman originals.
In my opinion none of these should be interpreted as depicting left-handed fencers, even if such images appear to exist as well.