AMD Steppings

[The Coolest]

I guess that what I'm going to write is already have been written or completely wrong :)

I think that AMD comes up with the steppings after the CPUs are created and tested for overclock right there (in the factory?) and by this AMD can tell what stepping to print on the chip

[The Coolest]

B U M P

[Tobes]

The steppings actually represent some minor change to the chip to cure shortcomings.
What each stepping has supposedly fixed is listed in the chip technical docs at the AMD website.

The speed rating of chips within a stepping are derived, as you say, by grading the batch.