All German goods wagons owned by the DR 192O (including those build since the 1880s) until today are covered by Stephan Carstens et al : Güterwagen Vol. 1-9 .
Very expensive but well worth it.- numerous drawings, photos, data und often modelling hints:
https://www.stefancarstens.de
Vol, 6 (brake vans) includes in depth roster discussions, and for example, half of the vans owned 1920 were Verbandsbauart standard
Stephan