Here, I focus on the variation of Pelikan 100N/101N barrels.

• As to material, it has been said that the barrel was made of celluloid (cellulose nitrate) until the material was replaced with acrylics in 1940. But, according to @stoen, there existed uncommon barrels made of cellulose acetate⁽¹⁾(e.g. model 100 in the 3rd generation (Fig.1), model 100N (Fig.2)). So celluloid and cellulose acetate coexisted for years. In 1939-1940, Günter Wagner utilized cellulose acetate for other parts (e.g. sections, barrels) to replace ebonite as the company did so with celluloid. But, beginning in 1940, acrylics took over celluloid / cellulose acetate in a stepwise manner.

• When celluloid barrel was introduced for model 100 in 1931, it was without any protection (Fig.3 top). The barrel soon got reinforced with brass ring (Fig.3 bottom). Model 100N had the reinforcing ring from the beginning. But, there exist 100/100N/101N barrels without ring (Fig.4 middle, 5, 6 bottom, 7). Without ring, the barrel is less resistant to crack, but sleeve looks tidy or clear⁽¹⁾. When acrylics barrel was introduced, reinforcing ring was not mounted anymore.

• As stated before, there exist barrels coated with white paint so that base barrel color would not show through the sleeve, most of which I know are tortoise shell model 100/101N (Fig.4 middle, 5, 6 bottom).

Model 100N produced in Milan also can be called "variation" in every sense. I'll comment on it elsewhere.

Note; ⁽¹⁾ Please compare the first year 101N and the 2nd year 101N (Fig.6).

⁽²⁾ According to @stoen, Some obvious advantages of cellulose acetate over cellulose nitrate are:

• possibility of both injection molding and machining

• being less flammable and more chemically stable

• being mechanically less brittle and less prone to discoloration

• not crystalizing at the junction with ebonite after more than 50 years (this is what we know now!).

Yet, it was a rather expensive and highly decorative material, so it’s unlikely that inner parts would be made from it (@stoen).