No. A missing imprint is not in itself evidence of a fake. The model designation was only shallowly stamped into the barrel or cap, and perspiration from the hand, decades of use and above all later polishing gradually wear it away. On many surviving pre-war and post-war models it can only be made out in raking light, if at all.
Identification therefore rests on other features: the nib stamp (585 or 14 C for 14-carat gold, together with the characteristic heart-shaped breather hole), length and diameter, the design of the filling system, the shape of clip and cap ring, and the colour and type of material. A black piston filler of this construction with a 585 heart-hole nib and an engraving on the cap belongs, according to collectors, to the family around the model 234½.
Anyone wanting certainty should put telling photographs before an experienced collector or restorer: the nib from both sides, the cap ring, the end of the barrel and an overall view with a scale. A remote diagnosis based solely on the missing imprint, by contrast, is worthless.