Everything about "pox leber" as a minced oath, and an earlier source.

[Koen G]

Perhaps a nitpick, but the Festnachspiele were late 15th century while Gemini refers to the 16th. This may be a normal AI 'inaccuracy'.
I also remember Anton writing that these terms were 'all over', which may have been an exaggeration, but it differs from Gemini's 2 counts.

I gave it a pdf of the Hans Sachs play of the "Peasant in Purgatory", which does contain two instances and is 16th century (1552). I have not seen any earlier attestations.