Bus 429, I can't explain the reasons, I can only sympathise. Roughly 60% of all my (KLM) transfers at AMS my bags have failed to accompany me to my final destination. They arrived a day later. AMS staff tell me this is an ongoing and well known problem which has been going on for years now! I wouldn't buy the bit about your bags never leaving HEL. They most likely got "delayed" at AMS.