Comparing the prototype with the production version, one immediately notices the "band" on the cap edge -- there is one on the production version where the "Parker" name is inscribed. The prototype has no such band and has no inscription of any kind as seen below.
Another area of difference, at least with this one prototype, can be seen with the cap tassie shown below. It appears that the tassie on the prototype cap has only 3 stacked rings instead of the normal 4 found on production 75 FPs. Thus it is not as tall as the production tassie.
