That has always been the case, Pelikan offered still from beginning of the production a lot of nibs for their fountain pens. In the 1930's and 1940's the following nibs, shown in the picture below, were available in the models 100 and 100N.

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Interchange of nib and/or nib unit among Pelikan model 100 and model 100N

Nibs are interchangeable only with other 100's. The same is valid with fountain pens from the line 100N. Nib units 100 and 100N are not interchangeable at all.
The model 100 is smaller than the model 100N. Even 100's from different eras may not have interchangeable nib units.
Nibs of the model 100N are same size as the Pelikan model 400 nibs of the era 1950/1956 until model 400NN of 1956/1965. Nib units but are different. They could not screw into other Pelikans.
But you might disassemble the nib and use a nib unit from a model 400.