Having once been involved with Helmet production I recall that after 7 years the EPS no longer provides the same properties as it did when new. I honestly don't remember the reason why, but I suspect it would be due to the loss of plasticizers over time. Whatever the case, I do recall that impact test results were noticeably worse and no longer met the standard. I'll come back with another posting after touching base with a helmet engineer next week with some better info, but the reason for writing was simply to say that if you are tempted to seek out a Bell V-1 Pro or similar ancient helmet, do it knowing that you cannot depend on it for the same level of protection it gave when new.
BB Bainbridge
Portland, OR