Anyway, I've just upgraded my front rotor and adaptor from 165mm to 203mm. My caliper is Avid BB7. Fork is Identiti Rebate.
Everything's fitted and working, but the pad hangs 2-3mm off the edge of the rotor so I'm not using all the braking surface. The disc and adapter are both 203mm, not 200mm.
I'm wondering if there is a thinner version of the "cup and ball angle adjuster funky washers" that sit between the caliper and the adaptor so I can move it inwards a bit more? I could use normal washers in place of them, but I can't imagine regular washers being perfectly flat. I'm not buying a new adapter when it's only 2-3mm out.
This is the kind of thing, where you go down to the local bike shop, and if they know you and are cool, you can dig through a box of brake pieces and rig up something that works--there are definitely bridges/mounts of different size and shape... I don't know about thinner "funky washers." I know that doesn't help much, but ...