The NBC was set up in 1909 as described on the TPA site.
In 1913, DER PAPER-FABRIKANT (Heft 5 1913 p135) reported that after lengthy negotiations, the New Bromine Silver Convention, which was provisionally concluded on February 15, is to be extended by 2 years.
The convention was itself a G.m.b.H. The members at that time were:
1. Albrecht & Meister A.-G Reinickendorf-Ost.
2. Berlin-Neuroder Kunstanstalten A.-G. Berlin W.9.
3. Neue Photographica. Gesellschaft für photographische Industrie m.b.H Charlottenburg..
4. Neue Photographische Gesellschaft A.G. Steglitz..
5. Oesterreichishe Photographische Gesellschaft m.b.h. Wien 3..
6. Photochemie G.m.b.H. Berlin N.113..
7. Regel & Krug Leipzig-Reudnitz..
8. Rotophot Aktiengesellschaft für graphishe Industrie. Berlin SW 68.
9. E.A.Schwerdtfeger & Co. A.-G, Berlin N 65..
10. Schönenberger Luxusppapier Industrie Felix Freund. Berlin N 65.
11. Heliophot. Kunstverlag G.m.b.H. Berlin N 65..
12. Kunstverlag Juno. Kunstverlag G.m.b.H. Berlin SW..
13." Bromsilber-Vertriebsgesellschaft m.b.h. II. Berlin SW 68..
14. Rotographie Belge, Brüssel.
15. Ungarische Rotophot-Gesellschaft Singer & Co. G.m.b.H, Budapest VI..
16. Wiener Rotophot-Gesellschaft Bluh & Co. G.m.b.H, Wien I..
17. Paul Fink, Berlin NO. 43 Neue Konigstrasse 63-64..
18. Gustav Liersch & Co. Berlin SW.48, Friedrichstrasse 16..
Another 1913 publication (Kartell-Rundschau ...) records the following additions:
Georg Gerlach & Co A.-G..
Hermann Trinks, Leipzig.
Thanks to Jean Ritsema for locating these documents.
Other members with example cards on this site, including pre-1913 members, are AVB (or VAB), BHH, CAES, FMK, GKVB, HSB, SPV, WKB, WSSB, Albert Horn and possibly others I haven't noticed yet. Also a member was the firm Ross Velag, which produced thousands of film star and related postcards 1919-1944. See the extensive catalogue on the ROSSPOSTCARDS site