There is really no need to run one of these guns by the guys at NASA to determine what its made out of. As has been suggested, scratch through the finish and see if it turns blue when you put a drop of cold blue on the gun.

I would use a little diamond burr on a Dremal tool. Under the grips, cut a little tiny divot in the frame. Just a couple thousands deep. If you can see a divot, its deep enogh. Put a drop of cold blue in the divot. if it turns blue, the gun is carbon steel that has been plated, almost assuredly it has been hard chromed.

Armoly in Fort Worth did TONS of cop guns around here. Stainless guns were very hard to find. Take your 19 and get it plated, it looks and acts just like a stainless gun. The color is almost an exact match for stainless.

There is the off chance it was mismarked at the factory. Possibly. Slight premium if someone wants a mismarked gun. I wouldn't pay extra for it, others might.

I don't think a letter will help either. If it was marked as a 19 but, was in realty a 66, I suppose Smith would still think its shipped as a 19 and, thier records would indicate that.