Bjoern Jacke <bjoern [at] j3e.de> seems to be the responsible for the German old and new spell dictionaries. You can find it at the top of the .aff files.
This is his page:
Ispell/Hunspell German, German Ispell Dictionary - Wörterbuch igerman98, Sprache: Deutsch
https://www.j3e.de/ispell/igerman98/
An English summary:
Ispell/Hunspell German, German Ispell Dictionary - Wörterbuch igerman98, Sprache: Deutsch
https://www.j3e.de/ispell/igerman98/index_en.html
Online spell checker
https://www.j3e.de/cgi-bin/spellchecker
The following lines are error free at his online spellchecker:
Halt’s Maul! Macht’s gut! Da gab’s keinen! Ich hab’s! Wie geht’s?
Halt's Maul! Macht's gut! Da gab's keinen! Ich hab's! Wie geht's?
What might be the difference between his hunspell checker / directory and the version in Sigil?