This would be correct, from their literature, but its possible there were some undocumented changes. However, I would guess the stainless steel nozzle you have is simply discolored.
As far as print quality, there shouldn’t be much difference, but the two steels conduct heat differently.
From Thermatest.com
The higher the k-value, the more heat the product conducts. Standard carbon steel has a K-value of 50, and stainless steel has a lower K-value of 15 .
In general, I’d imagine the hardened steel is heat treated carbon steel. So this would suggest there is a significant different in heat transfer with the hardened steel nozzle which will generally allow better and fuller melting of the material along with improved Z strength. For reference, I believe brass is in the 110 K-value range, so even though hardened steel is better than stainless, its not nearly as good as the standard nozzles.