Hello Jan,
please don't await too much from the "Geschlechterbuch".
The "Geschlechterbuch" is a possibility to get printed your family History.
You may sent your manuscript to the editor and he will print whatever you
want, because you've paid for it.
I found there some genealogies which were (carefully said) not so very well
done. Especially in the older volumes ....
Of course there are also "good" Genealogies in these books, and it's almost
impossible for an editor to verify the content of this kind of publications.
If you don't find but a name, a volume, and a single pagenumber in the index,
you often will not find but a marriage date. So it might be better to have a
look at the book before buying it.
Brigitte Jahnke