The cassette I just took off was brand new when I put it on, and actually the crush washer was deformed in the package - not to the extent of the one in the picture, but it had some indentations on it. Again, brand new never been torqued. If someone at Shimano grabbed the wrong washer, they've done it three times now with the three new cassettes I've put on this bike.

Re-using it is what this conversation is about... I really don't think it's a good idea, but I can't find anywhere to get new ones, and both PedalWench and SK think it's fine. I haven't looked, but probably I could mail order them from the UK, like the parts to rebuild the brifters.

I didn't try hammering it flat, that's an idea for next time. It doesn't appear to have a front/back that I can tell, but I didn't remove it from the lockring when I installed the new cassette, so again, it went on in the orientation it was in the package. And I torqued it to spec with my good Snap-On torque wrench.