[Illsteir]

Spoiler for Theory:

After reading the 00F manga and 00P photonovel, I came up with this theory:
In the photonovel, they said that the GN-000 O Gundam is the first generation of GN machines, GNY models (the prototypes of the GN models, the GNY-004 Plutone is included in this generation) are the Second Genaration and the GN Models (The 4 Gundams in the anime) are the 3rd Generation.

And in the manga, When Fon Spark insisted on using the GNY-004 Plutone instead of a mass produced GNY-001 Astrea, Chall Acoustica reacted. Probably because the machine has an unstable feature or there's something else. CB probably ceased the production of the GN-004 because of that reason.