A helmet, much like a kevlar vest, is ment to defer impact energy not iliminate any injury. A helmet, if I remember right, is tested for impact force in a typical six foot fall, not when being struck by the fender of a '67 dart doing fourty. Far more people fall off their bikes on to the curb than are hit by cars. I have crashed hundreds of times but only hit by cars twice. First time multiple femur fracture(No helmet on my thigh) Second time, hit by pickup, kissed pavement going about 20, destroyed helmet opened both knees and elbows, lost about a half pint but no concussion. Highsided my Kz at 60 plus, messed up a good set of leathers and cracked my helmet but I walked(limped) off with only a bruised knee. However, I got heel kicked in the head during a competition, viola', concussion. Nothing like having your teammates walk you around all night when all you want to do is take a nap.
You can always trust a "court specialist", they would never lie, just because they are paid to have an opinion that favors a certain outcome
Read here about Saami Shaibani an expert witness in many cases finally called out in a local murder case.
http://www.newsobserver.com/peterson...-2669833c.html