Well covered guys
I lost a dear friend to a single motorcycle accident. He was drunk, missed an easy corner & ran into the curb (No helmet, no helmet law). I talked to the shift commander about the accident the next day. He informed my that sometimes, like in this case, a helmet would not have saved him because of the severe deceleration of the brain matter inside the skull.
So whether there is a difference or not on the ability of an older helmet to absorb the impact may not matter. I'm not so sure it's going to make a difference if my six year old helmet will save me from the big one. Each situation must be judged individually.
For those that fight for it, freedom has a flavor the protected will never know.