The Delta Flyer II is used in this episode, but in the next episode Harry and Tom take it on a "test flight." Clearly Drive (2000) was meant to air before "Imperfection."
Seven states that her link to the Collective was severed "nearly four years ago." It's actually just over three. She joined Voyager's crew at the beginning of the fourth season.
There is still a Borg corpse in Voyager's sickbay's morgue, presumably with a cortical node; however, as The Doctor states after the failed simulation, that one would have been inactive for too long.
(at around 7 mins) The edge of the nude-colored sleeve that simulates the implants on Seven's left hand is visible.
After her initial examination by The Doctor, Seven reminds him that members of the crew are entitled to doctor-patient confidentiality, and the Doctor agrees; however, The Doctor would be obliged to warn the Captain if a patient's condition threatened the safety of the ship or affected the crewman's performance, something the Doctor should have pointed out before agreeing to keep Seven's condition to himself.