any mechanical, however bad should give corret readings from the quadrature detector. This with the obvious exception that if the mechanical problem is between the machine and the encoder, all bets are off.

I have with VERY sloppy mechanics read the same at the index in extensive tests.

FYI when you see the index, the count should always read the same, regardless of stops and starts, and be reset then. This is the only method I know of to verify encoders.

Erik