The online help has schema diagrams, check there first.
You can also show them the data models task, that has a lot of detail on linking.

I have no idea what you mean about degenerating a generation, but maybe you mean you want a tool that can map the entire database and produce a diagram as you see fit (filling the gaps where Sage hasn't provided diagrams)? In that case, you might also have a look at an ERD tool, such as Embarcadero Studio. Last I looked at the tool, it could discover relationships based on key values and then deliver a diagram accordingly.

Hope this helps,
Bob

You can try  Sage X3 Online help center searching "MCD", "Data models", etc ...

Or you can check here for instance : Data Models for Sage X3

I am afraid not...
But if you click on the tables the details seems up to date.

I think you need to ask Sage for it.

I also saw there was an Idea and I suggest you to vote for: https://www.sagecity.com/us/sage_x3/i/documentation__translation/data-model