Pelikan was the first company to implement the differential piston mechanism that allowed the piston to move faster than rate in which the piston knob was turned. This allowed for faster, more efficient filling. This piston mechanism was introduced in 1929 and is still used in all of its Souveran series fountain pens.
In the 1950’s, Pelikan introduced the model 400 which had green and transparent stripes on the barrel that looked like the striped pants of a Stressmann style suit, and thus this model was nicknamed the Stressmann. All Pelikan pens that feature that striping pattern are referred as such. In the 1980’s they introduced additional Souveran series pens.
There is already a great resource out there that gives excellent information about vintage Pelikan models, Pelikan_collectibles.com, which we reference here:
Fig.1 100 Model in green celluloid
Fig.2 100N in Lizard finish.
Fig. 3 Pelikan 400
Fig. 4 Pelikan 400N
Fig. 5 Pelikan 400NN