If I remember what my uncle the airplane restorer told me they used to use both. You would start with the nitrate, don't remember if it attached fabric but do remember it was used to fill the fabric because it filled faster than butyrate. After that the plane was finished with butyrate, usually the silver and then the color. The silver was used for UV protection and an undercoat for the color.

You can do models the same way but butyrate is hot fuel proof and nitrate is not. I have mixed the silver with powder and used it for an undercoat and it does make some colors look better it seems but it takes a lot of dope around to do all of that.

Cliff