AMD officially uses the expression "Stepping BA" on its site:
http://products.amd.com/en-us/OpteronCPUFilter.aspx
but yeah I think that it may differ from CPU-Z showing.
On Anandtech, K10 2.5GHz ES shows stepping 2 on CPU-Z,
and revision is grey-out.
I suspect 2.5GHz ES may be "Stepping BA", only just speculation.

Anyway I still have a little, a very little hope for newer stepping & BIOS