Now, what I
have found is that the chinese caliper, for exqample, is in fact
accurate to the stated 0.0005 (used a $125 USA to check the three I
purchased for $15 each).

No, they're not. calipers by their very design are not accurate to .0005.
Yes, that's what the dial reads, but if you're trying to get closer than a
couple of thou, you best be using your mikes.