The online Calc help topic "Addressing by Name" says "Range names must not
contain any spaces" and adds no more constraints. The Calc topic "Recognizing
Names as Addressing" says "If you want a name to be automatically recognized by
Calc, the name must start with a letter and be composed of alphanumeric characters."

The fact is that a defined name can be alphanumeric and use the following
symbols: underscores (_), periods (.) colons (:),  dollar signs ($), and
question marks (?). This I found out through trial and error.

Labels it seems can be comprised of generally any text, but I am not positive on
this...and the help is of no help. 

The help should be more explicit in what *exactly* are the allowable characters.
 Issue 40569 also seems to address this from another viewpoint, but this is by
no means a duplicate.