We call it an NC because that is what is written on the model reference when the back sticker is intact and filled in!

The Monacos pre-date the other PVD watches - this is clear from the serial numbers involved. The next PVD watch we see is a barrel Carrera and its finish is quite closely reminiscent of that of the Monaco, at least in the earlier watches. Later Carreras are rougher and more like the Montreal and Monza as Heuer experimented with particle size and additions to the PVD to improve adhesion and wear.

To me, it seems most likely that the Monaco was Heuer's initial experiment with PVD and never made it on sale because of problems with PVD adhering to the edges and excessive wear, as you say. It's quite telling that the subsequent PVD watches had much rounder cases without such sharp edges.