I just ran into this situation.
We were rear ended (again dammit!) with a Britax installed.
One of the Tech's from this board did confirm the accident fell under NHTSA's guidelines and could be in continued use.
I was kind of ok with that. Britax seats are tanks compared to many others...
As I got to thinking about it, I decided I was not ok with it. A real small fender bender, etc. and I would allow it (stretching maybe even to other manufacturers seats.) We got hit this time by a semi truck at a red light. The force at which we were hit was comparable to my rear end over the summer. That rear end did do some serious damage (to me, to my car) to my MyRide. A simple rear end caused the entire rear facing belt path to be WAY stressed/warped.
This Britax was also a hand-me-down (from a trusted source, no accidents) but it got me thinking on how much "damage" the seat may have accumulated from normal use/installation/storage plus the rear ender.
I know I pissed off a few board members by asking how to get it replaced by insurance, but I honestly would not trust my child's life in it now. I think many of us, viewing it that way, would agree that if they did not feel trust in something they wouldn't have their children anywhere near it.
Our insurance IS happy to replace it, thankfully, and will be seizing the Britax from us shortly.
I think we need some modified and universal guidelines.