I found another "poxleber"

[Bernd]

I still regard the expletive hypothesis as highly problematic, maybe even more so after this genre confirmation. 

• LFD, Marco and myself are in agreement that the You are not allowed to view links. Register or Login to view. handwriting points to a period roughly contemporaneous with that of the radiocarbon dating. 
  
• Both attestations have identical genres, which could not be further removed from the genre of "scribe's marginal annotation in an early 15th century codex".
  
• The impact of the oath is not just that of "goddammit", which has lost all impact on us. To feel the impact, think of the must vulgar curses you can imagine in your language.
  
• The 15th century reference to pox-swearing I found earlier is a strong condemnation thereof, in the spoken language of the commonfolk (does not mention "leber").
  
• As far as I'm aware, the full expletive includes the "so mir" part (sammer, sommer, whatever). We don't know if anyone was yelling "pox leber!" in isolation. 
  
• OCR heavily skews towards printed texts, increasing our chances to find the (still rare) 17th century uses. 
  

And perhaps most importantly: even in the 16th century, "poxleber" is only used in dialogues. The author does not say "So mir pox Leber, ich liebe den Pabst nicht!". He has farmers say it, or even the decadent pope himself.

Valid points.
I still consider the hypothesis that the author of the marginalia was the VM artist as a valid possibility. Which also does not go well with a 16th century setting.
However I'd like to point out that we are dealing with very unusual marginal annotations. Which do not look like they were produced by a scribe. But rather by someone who had quite some trouble writing. I am aware that the poxleber expletives were - heavy. But considering the VM was likely a personal project and the person who wrote it (or at least made the drawings) might indeed have been - of rural origin, I would not rule that out. We have very little personal notes from 15th century barely literal people. Still it is odd that Hans Sachs and Niklaus Manuel Deutsch used this same swearword. What connects them is the same time frame, genre, religion and political view. What does not connect them is geography. Hans Sachs was active in Germany and Austria and spent some time in Innsbruck, Tyrol. Niklaus Manuel was in Switzerland and Italy. The fact that both used the same term in printed works rules out that poxleber was a regionally confined variant.
So what gives? Both wrote popular Fasnachtsspiele for common folk. Sachs lets a farmer swear, Manuel the pope. Obviously the usage of this term was discouraged and should label the character as extremely vulgar. Where did they pick it up? Was it just a popular swearword at this time in the early 16th century? Or was it a generally used expletive that simply was not recorded in literature before?

All in all, I'd say we still do not have enough data to decide whether we are dealing with a minced oath or animal parts in the VM. The drawings suggest the latter. But VM drawings suggest a lot.