SAS seem to have some strange rules on carseats, it would appear from their website that the maximum dimensions are those of an infant bucket seat which wouldn't be much use for an infant over a year (at the max) do they still not allow the CARES harness?
If a car seat is lost is it not treated the same as a piece of lost lugggage? i.e can be claimed for?

Usually not. It's considered a "check at own risk" item.

Foreign companies do not guarantee that a car seat can be used on board. I've never flown SAS with a child but car seats were taken from me on numerous European companies. That's why I always tried to fly U.S. registered companies when I flew long haul but that wasn't always possible.

BTW, sounds like SAS totally trumps Air France on short haul. We never got anything like that on any of our many flights on them!