Car Seat Update
As I mentioned, I received an initial response asking for a receipt for the old car seat. I looked for it a bit, but could not find it.
Now, today, I received a form letter from Lufthansa with the full amount of my original claim for the new car seat the the other supplies we purchased.
According to the letter, a check for about $189 should arrive in about 14 days.
Hooray for Lufthansa! (It seems quite likely that it was US Airways fault that anything was lost at all.)
cobberjoe