So at the end of operation interviews it's implied that wally, kuki, Hoagie and abby remained in the knd as adult operatives or whatever. If you disagree with that interpretation, suspend your belief for this headcanon. So this implies that they were all in the tnd. And abby was the only one put.of the four that knew the tnd existed; she found out from Maurice in an onscreen episode, this is definite. Now skip back to when nigel left for the gknd, sector v was devastated. I think it may have made them realise they were all going to be decommissioned, and at that moment abby revealed the tnd as an avenue of escape for them. This subsequently caused sector v to train really hard to improve their skills so they could join the tnd.