This is an odd one that I found. No, it is definitely not a prototype since I have the full packaging as shown below.
The "Lifetime Guarantee" sheet that accompanies this BP have are dated "4-64" while the price tag has "10-65". In my discussion with other 75 collectors, we think that this conical tassie may have been a transitional and intermediate tassie form before Parker decided to go to the dished form. One collector even has this tassie on a fountain pen!
Since this conical tassie is not found "in the wild", it is quite probable that Parker only used this for a very short time, perhaps only for a few months. My guess is that it appeared in late 1965 through early 1966.
I have received email from people to indicate that these were found "in the wild" at various flea markets, antique stores, etc. from different parts of the US and abroad.