Hello Crezac,
regarding corrections in the text, there are several instances where we can see that individual characters in words have been emended/ overwritten/ added.
Over the years, I can't remember what blogs I've seen these on but one example that comes to mind is the often discussed "der mussdel" (or whatever it actually says) label near the lady in f66r, where the characters have been overwritten.
There are other examples where the author(s) or someone else has gone back and made various corrections and emendations to characters. One recent discussion of such an example can be found here on user JKP's page:
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I really need to go now but will try to find useful links about this later.