I’ve not seen a case where the NPC estimates, say, 12k and the student has to pay much less- it could happen but I wouldn’t count on it.
The reverse happens, especially when costs of living are factored in through ISFAA or CSS questions at meet-need colleges (an income of 80k goes further when average income is 3k a year than when the average income is 30k a year).
So if the college is too expensive as per NPC I don’t think there’s much risk in thinking it’s not going to work financially even if the NPC only estimates for US citizens.
At public universities that differentiate between in state, out of state, and international tuition, it can also give a good understanding of extra costs or guarantees required for the institution to issue the I20.