Neil,
I was recommending that you work through the process. I wasn't trying to be negative. It's a little bit like reading a book on sailing versus getting your a$$ wet on small boat by experiencing the real thing. Also I think you have a bigger picture in mind than your tables in your database reflect. You're doing great and Bob's stuff is right on target.
It can be difficult to build a database and then add new features that were not accounted for in the original design. You can design a 3 storey house and build the foundation and first floor. Then build upper floors later because your design identified the things in context. Anyway, it's a would-be-nice-to-have rather than a mandatory.
You're doing fine --carry on. Good luck.