Lost luggage.. outbound and return !
 

Lost bags - twice.

First route: AMS-x/OSL (KL)-x/IST-BKK (TK)
After arriving in BKK, I was notified immediately that my bags didn't make it the flight. I was led to believe that the bags were left in IST. It was eventually returned 4 days later and after going through the bag tag documentation myself concluded that the bags were left behind in OSL and not IST as I was originally told.

Return route: BKK-x/IST-x/LHR (TK) - AMS (KL)
No bags again. This time KLM couldn't even tell me where they are. However the lounge agent and I somewhat agree that it was most likely left in London Heathrow since that airport is infamous for lost baggage and this being Christmas Eve, baggage transfer service might be lax.. even with a 4.5 hours transit.

I don't expect to see my bags till after Christmas.

So what is it with TK?? All sectors in Business Class, *A Gold status and KLM in Business Class too.

Yep. TK left the bags in London.

KLM has found them and are on their way to AMS today.. on Christmas Day.

Does TK and KLM have luggage interline agreement? From the story it seems the challenge was more with KLM than TK, potentially because of missing/not well documented interline agreement...

I would be more inclined to the 'baggage interline' agreement theory actually.
since it has happened twice ...
This year I had my bag lost at least 3 times ...same airlines LH and LX ..

Most major scheduled airlines have interline agreements. If they don't they can't issue the baggage tags at check in.

Hopefully you got nice suit and shoes and upgraded your fragrances ;)

My insurance only kicked in at 6am Christmas Day. This being the Netherlands , nothing was open.

You should change your insurance if it doesn't kick in after 4days of luggage lost? Or was it your homebound sector?

That's the return sector! It's 12 hrs from arrival. I landed in AMS at 1705 on 24 Dec.