I'm not after a fight with anyone either

I think it's all down to the extent of any force applied to the lid, dropped from a foot onto carpet it's gonna be ok .
Dropped from 8 foot up onto concrete it's likely to take some damage.
Although the shell is hard it will distort when enough force is applied and compress the liner on the inside next to the shell unseen and thats the problem you can't really tell how much of its shock absorbing capability has been used up.
lots of people hang the lid on the mirrors (guilty) but that's frowned upon as it can damage the liner with just the lids own weight.
Of course manufacturers and sellers are going to push the scare side of it to sell more lids, I read in a mag the other day that your supposed to replace the brake caliper mounting bolts every time you take them off as torquing them up distorts the thread and a reused bolt is more likely to work loose! How many people do that?
Personal choice will determine if your comfortable with using a lid you've dropped yourself, If my lid got knocked off a chair onto the floor then yes I'd carry on using it but if I dropped it down the stairs?
As to lids failing after the first hit in an accident again it would depend on the force of the second impact, most of the liners protective capability would have been used up in the first significant hit. would also depend on if the impact was in the same point on the lid.
The shell is there to spread an impact over the lids surface and the liners job is to slow down your head movement to try and not rip the blood vessels and nerves attached to the brain and thus prevent brain damage. Hopefully
