Collective printmaking ?

A Printmakers Puzzle 

This posting is about a something that is bothering me and keeping me busy for a long long time. To be more precise: prints by printmakers I can not find anything biographical about in the Internet, Artist Index or reference books and prints that show too much similarities to be just a coincidence. I ask the help of readers to solve this mystery. Is it the output of a printmaking collective or are they printmaking friends, a school perhaps ? The signatures however seem to be written by different hands. 

Print collectors and other enthousiasts must have noticed certain similarities following the works of these printmakers. To begin with: 

Thea Gütmann-Voigt 

(these 12 prints by her hand, two of them with a monogram TG): of all printmakers I've been researching it has been to this day impossible to find any clue or anything biographical about her. Gutmann or Gütmann is a Jewish name but it could very well be she was born as Thea (Dorothea, Theodora) Voigt. The Thea Gutmanns I followed leading to no identification yet. 

As goes for these following names/artists (or could it be one and the same ?)  

W. Neumann 
(or is Hermann ? 10 known to me examples)

 

Ruth Lundbeck 
(three examples known to me with this signature )

  A(?) Thies 

(or something similar, just the 1 example, these Poppies are known to me).

and ?.?. "Colmsz" (or something similar, 4 examples) 

The prints I've seen and in some occasions collected (not all !) are mostly printed on identical papers, are very similar in style and execution, and in several cases prints with different signatures were equipped with the same blue wove backing paper, although in three different shades. In one occasion prints were kept and send in this rather nice paper-folder with "Japanische Holzschnitte" (Japanese woodblock prints") in calligraphic writing. 

It has happened prints by different artists (different signatures) were sold together in one lot. And with one exception: they all are, kind of, botanical prints: showing flowers.

In any case with this posting from today there's now a reference on these rather nice prints available. All help, additions and suggestions would be most  welcomed.