Voyager was lost in 2371.
First contact happened in 2373.
Scorpion happened in 2374.
Seven of Nine knew about the Borg's involvement in 2063.
They wouldn't know that Voyager had something unique to offer until after they'd popped the hood, and they're not going to do that unless it looked like Voyager had something to offer, which it probably didn't since Voyager was at least 2 years behind the most recent ship which they had assimilated in First Contact.