The EMH was last activated prior to Voyager leaving, there's no reason to think his program is periodically updated with current events while he's inactivated.
Back in the 90s it might have made sense that their computers would take time to be updated with that sort of information. Even today, the most common paradigm is sharing information via some central server.
But Voyager was docked
at the station which had the most intelligence on the Dominion there was to have. Realistically, their computers should have synced that data automatically so it would be available as needed.