After you file

on the 1099-div form enter the CGD on line 2a of form 1099-DIV if it is not already there.

when you imported was the 1099-Div completed? with some brokers. importing the 1099-B is one step but the 1099-DIV can be a separate step. 

each broker has their own method for importing documents. for example, one broker gives you  a choice of what forms to import. if you want them all each needs to be checked off.

 

have you checked with Vanguard to make sure the 1099-DIV is available for import? with some brokers different forms s come out at different times.