Good Morning Michael & a Very Happy New Year!
Wonderful reference, and I thank you for posting it. The deeply curved belly of the 3rd example in the 1st panel (counting left-to-right, top-to-bottom) does indeed resemble our "mystery dagger" in blade profile.
Considering the fanciful appearance of the cut out work along the blade spine in this illustrated example, I can't help but think that if it existed, then Bosch's dagger likely existed as well (especially in light of the other reasons discussed in the thread). Given the details which seem to indicate he painted the same dagger in two of his works, I have to wonder if he had some personal connection to this particular dagger...
Do you by chance have larger scanned copies / images of these pages available? If so, I can PM you my email address, as I would like to have them on hand for reference. I find the turned wooden grips to be interesting, as well as the exposed tang on a couple examples (that appear to be twisted?).
Regards,
Chris