Hi if your topic is solved please consider turning the topic as solved see Q&A New Functionality.
In addition to the @mp5gosu message I wanted to point you to the NodeData::Write/Read/CopyTo for more information see the C++ NodeData::Read() / NodeData::Write() Manual which will handle to write/read data when c4d close/open a scene.
Moreover, if you go to the BaseContainer way and still facing issue with data loading, you may need to react to some message, see NodeData::Message.
Finally, if you implement the Read/Write make sure to use the disklevel functionality when you register your Plugin. Disklevel can be understood as a plugin version, so if you modify the structure of the data stored you will still be able to read/write your data according to the correct version.