Seven receives a little more backstory concerning her history in the Borg Collective in this episode, and it's both surprising and ironic, calling to mind a third season episode ("Unity") in the process.
It seems that Seven once experienced a brief moment of separation from the hive mind, along with the rest of her unit at the time, and she's the one who fought it the most. Years later, in the present, she reunites with these drones, who've also since permanently left the Collective behind, and it turns out she's had better luck severing the connection.
Some convenience is necessary to make this one work, but it's a welcome return to the kind of Borg storytelling that works best in this particular Star Trek, and casts an appropriate glance backward for Seven as well as foreshadowing for later developments in the season ("Collective").
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Memory Alpha summary.