Yes, I do know we have to pick up our luggage to go to customs in Seattle. But it's still much easier if it's checked through because you can just hand it back off. One time we didn't have it checked through and had to take it to another terminal to check it in. But we do have plenty of time in Seattle for whatever. The most important would be to have it checked from Zurich through to Seattle.
I agree this sounds like it's up to KLM so should be in the KLM forum. Hopefully it gets moved.
Do you think there is a difference between whether we book KLM or KLM Cityhopper? The Cityhopper leaves 20 minutes earlier which could be helpful.