Seven of Nine had full knowledge of what went on while the Borg and the Enterprise were in 2063, as she made reference to it several times throughout the show. That clearly shows the Collective would have known about all that stuff, including the uniforms, during the events of Scorpion. Which given that's when Species 8472 first learn of Voyager, Starfleet and the Federation it would have to have been during Scorpion they would hypothetically check out Borg computer files about Earth and Starfleet Command.