I found an alternative approach, a work-around, not sure it helps. See attached. When save as pdf, the 2nd line of the "date" shape will retain the Visio creation date.
The approach was to create a shape data entry for the creation date. Then, create a user defined entry, that uses GetVal fcn to access the shape data entry. I suspect it's a timing thing, but, the result is that user entry displays the correct value, even though the shape data, directly, does not. Just lucky I guess.