For information about bicycle helmest, I commend http://www.bhsi.org to you; I think it covers everything except history rather definitively.
History (within time-line): I know of two true protective helmets before the Bell Biker. One by MSR (Mountain Safety Research), and featured a web suspension. The other, Bailen, was Australian. I was sent an MSR to evaluate about 1973; it came out within a year. I think that the Bell Biker came out after 1975, but not sure.
The Skid-Lid was not a protective helmet. Hair-nets and Skid-lids offered nothing except abrasion resistance.
The primary function of a helmet is to absorb shock, slowing the head's deceleration. In practice, this requires rigid foam. A good helmet will reduce the impact of the brain against the skull, which is what causes concussions. 600g --> skull fracture; 300g --> concussion.
I was told that Skid-lid declared bankruptcy immediately after the ANSI Z90.1 standard was adopted for rating bike helmets. There was no way in Hades that the Skid-Lid or other soft helmets of the era would pass this "drop" test. Bankruptcy protected the owners from litigation from those harmed by trusting the helmets. The ANSI process had been going on for several years, and it was already common knowledge that the S-L was useless for the intended purpose.
I have a Cinelli or Kucharik, a Skid-Lid, and several other "real" helmets. I am missing an MSR, if anyone has a spare.
thanks,
harvey sachs.
mcLean Va