It has been quite a while since somebody was working on this challenge, or at least it looks like.
I am native German and had a look at the text and the historic surrounding.
Starting from the beginning, some members were working with the assumption, that the authors has to be a writer, because he has written a book. That has not necessarily to be the case. As from my own experience as a civil servant is Germany I know, that quite a large number of my old colleagues used to write a book after they retired and published them. You will find a lot of expert books in history written by government officials or high ranking members of administration. This leads me to my working thesis, that the author of this book was not a writer of prosa, such as the mentioned “Schicksale der vermeinten Gräfin…” but somebody who had to deal with encrypted letters in his job, such as a member of the secret police or maybe a notary with some side income. Reading the book of Umberto Ecco “The Prague Cemetry” gives you a short impression about how information was dealed and transported in that time and society. So I am not looking into writers but members of administration, which makes it even harder, because they are not so well known.
Another trace I followed was the fact that he mentioned the “Blumensprache” but that could be well known that time, so maybe not a real trace.
He stated himself at one point as “Herausgeber” and not as “Autor”. Herausgeber is a person who prepares a text for publishing, written by another person. So by using the term “Herausgeber” it is on top unclear if our mysterious person wrote that book or just prepared it for publishing. If he wrote that book, then why he calls himself “Autor”?
Something else which came in my focus was the “Konkordientag”. I could not find any reference to it, so it seems like this is a term not really used in modern German and I found only one reference in Google. Seems to be that the 18 February 1648 was one Konkordientag. It seems to be a term of the christian protestant church. Since he mentioned lots of time the Iluminati and keeping in mind that there was a lot of conspiracy going on these times, it might be possible that the writer was part of a clerical administration. But we have to keep in mind that even non administrative people were busy in the field of conspiracy and espionage.
In his opening statement he writes about different types of encrypted messages, like notes, letters, protocols and so on. So again I think that the unknown author is not just a writer, but somebody who dealed with decrypting letters in his job, so he had knowledge of all these different kind on papers and methologies.
These are the fact I found out yesterday. Don’t know if that will help, since as I said earlier it could have been written from anyone in the higher society such as civil servant, secret police, church administration or even a notary or any other person who was busy in the field of conspiracy.
As for now I want to try to find out more about the so called “Konkordientag”.