Thanks all. This is the response I received from KLM: "Hi! Some local authorities demand that passengers must be able to show a negative COVID-19 PCR test result. These demands are not imposed by KLM, but by the local authorities. Therefore, I strongly recommend that you always contact the local authorities."
It seems that no one actually knows. It is encouraging that ClipperDelta was ok without a test. Not sure what I will do, other than hope there is more clarity before I fly.