I wouldn't say the silver dial printing was diagnostic in and of itself of an early watch, and would thus hesitate to ascribe more value to it. In conjunction with other tell-tales though (poly caseback, Ed Heuer bridge) as on Arno's watches, then it's easier to be definitive about it being an earlier watch. The serial number, given everything on the watch being original, is then the clincher.

If we take the Dato 12s as a case in point, we do see some "mid-term" dials coming out with silver dial printing.

And then moving on to NSes; as I alluded in my reply to your two-reg question ( http://www.chronocentric.com/forums/heuer/index.cgi?page=1;md=read;id=38606 ), none of these are likely to be early watches. So I think we're seeing the effects of Heuer and their dial suppliers playing around with different dial finishes over time. I've corresponded with other forum members about how there seems to be at least two distinct batches of SN dials - the same could be true about the NS dials too.

Jeff's point about the S dials is interesting too ( the earlier ones with "flat" white paint and the later ones with the white / silverish "starburst" finish ). The "white" dials have an almost enamel-like finish (that I've seen crack like enamel on rare occasions too), whereas the starburst dials are pretty much out and out silver as far as I'm concerned, going further than silverish. The difference is even more obvious when the dial has one of the specialist scales on it too, with the scale being on a very distinct "track" on the whiter dials and blending more into the rest of the dials on the silver ones:

We did discuss some of these details when we were working on the Carrera table, but I think definitively dating and including them all would have been the devil's own job and we might never have finished! And it would give us less to talk about after the event too :)