NPBs stay permanently for both buying/selling, I have some from 2021 still in
my "orders received"
I think that's how the strikes are enforced, if the order disappears the
strike doesn't exist; I may be wrong though
I'd say you're right.
If you still have some (NPB/NSS) - no judgment about this, you just bad people
- then they've not been removed and they'll count in the max 3
you can get before priviledge(s) removed.