Perhaps more critical, the flange diameter.
Eccentricity is your enemy alright, but if the flange
on the ring swims in the subbase counterbore, you're worse off!

Not positive on the error you're talking about.
Wall thickness or OD?
A variable wall thickness is innocuous. A screwed up OD can be a problem.

Centering your ring to the cutter, an issue?
See:
http://patwarner.com/precision_subbase_kit.html