Thank you for the valuable information.
Implementing CreateSceneFromC4D() appears to be what I am missing. Since we never cared about skeletal transforms, we were relying on, as you put it, the fastest way to extract the actual geometry of the object, which was working really well for the previous simpler cases.
I'm currently working on other tasks, so, I haven't validated everything yet, but this seems to be the solution. I won't hesitate to ask if I run into other problems when I return to the importer, but this looks doable now. Thanks again for the help!