Changing the Format of a Graph Legend...
 

....I'm not even sure how this is done normally, never mind
programatically!

I have several graphs in BookA which are linked back to BookB.
If BookB is open then the dates in the legend are formatted "August",
"July" etc. but if BookB is shut then they are formatted as numbers
"38930", "38961".

How do I programmatically change the format of these legends?

Any help greatly appreciated.
Jason.