For intra-European V and N fares, the KLM website states:
"Airport taxes that are not used can be refunded. The fuel surcharges mentioned with tax code YR/YQ are non-refundable if a non-refundable ticket was issued."

This statement does not show up when you look for an intra-European E fare,
so maybe they are more generous in these cases.

I think this is a recent development.