Thank you. I will pursue this further. However, I have a question:
Is this so? Technically, I have not accepted the voucher, they're sending it to me anyway. Also, during the 6 hour wait, every passenger received a small set of vouchers for 2000 KLM miles, €50 off a future KLM flight, €10 to spend at the airport, a phone card, and as mentioned a night at a hotel in the US including transport while waiting overnight. I submitted the 2000 miles voucher already, but didn't use any of the other vouchers. Does this mean I am ineligible since I "accepted" the 2000 miles voucher?
Don't worry. Under EC261/2004, airlines can only offer miles/vouchers in lieu of compensation with the formal consent of the passenger. The phone card/food voucher/overnight accommodation are part of the mandatory assistance carriers must provide. You can get the miles credited and pursue your claim for compensation without problem.