Each config entry (for weapons, vehicles, units etc) has a library class, as such:
class Library {
libTextDesc = "$STR_LIB_M16";
};
Which determines the "library text description" that you're looking for. The actual string it's referring to, however, exists in a stringtable.xml which, I think, can usually be found inside the same .pbo as the config, or if not, inside the ca.pbo. Don't quote me on that, though. If an addon does not have a description, it's probably because it's missing the above class in its config, meaning you can fairly easily add it. If you're making your own, I believe the text can just be written directly into the config as well, you don't HAVE to have a stringtable for it.
But yes, to be able to 'fix' this, you'd have to do a lot of config searching, replacing and so on. You could -maybe- create a replacement config that would replace just the above class with your own descriptions, but once again this will be a lot of work.
Wolfrug out.