Very, very cool! Really makes a guy wonder where that lost PrePro1 has gotten to.
If it did become the ESB or PP3, then there is another helmet out there that we don't know about and haven't seen. It it didn't (and I suspect it didn't and is still the "ears" helmet to this day), I really wonder where it is. The sad truth is, we just have no clue.
Yes--Art--thanks for compiling this into an easy to follow graphic. Very interesting history.