David,
Not sure where you are getting your information but it is incorrect.
A Baseline can store any set of data, related or otherwise. They can
include CAD Docs (parts, drawings, etc.), Docs, Parts, Change Objects,
Requirements, etc. You can add to them using add, paste or collect.
Attached is a sample flow starting from a drawing in 9.1 (process is the
same for 10.0)