The airline will ask you what you have in the luggage and value of those items when the luggage goes missing. Unfortunately, the usually will need some receipts to determine the value of those items.

Check this section out:

http://airconsumer.dot.gov/publicati...ts.htm#baggage

Maybe check what are your rights in US with a lawyer. Then negotiate with Thai thereafter.

Personally, I would not take the offer made. I think it is way too low.