I still think that socket was made when SK and Facom became one. It makes sense that you found it in France.
i can't believe you guys are still talking about that socket. other than the fact that it has the letters s and k on the socket it has no other things that would make it an sk socket..
1. it has a satin finish. sk has never, at least in recent history made a satin finish socket.
2. it is marked s+k. sk never used the + symbol in any other marking that i know of. sk was owned by facom at the time you speak of and it for sure was not in use at that time.
3. if you look closely, the s and the k are lower case. if it was marked S+K you may have a leg to stand on but lower case, no way.
4. they are marked chrome vanadium. something else sk never did.
if someone can show me any sort of proof those were made by sk or even facom i could be swayed but i highly doubt either sk or facom would stray that far away from either their own logo or style.
my guess based on the statements above is that s+k is some sort of european brand that was just using their own brand or logo on some private label tools. they probably did not even have knowledge of sk and it's history as it is not a well known european brand.
No brand name=no warranty overhead. No brand name= less likely to walk off/get stolen. There are so many inexpensive socket sets available why buy mystery sockets? 
