Thanks for the help. I found this on finishing.com:

"A strong possibility is that you sometimes get 304F instead of 304 or 304L.
The F grade has a high sulfur content for improved machineability, and
etching on any plane that is not parallel to the rolling direction from when
the material was originally hot-rolled, will give the sort of finish you
describe. The sulfur forms discrete particles of manganese sulphide in the
steel, which elongate with the steel during rolling. On any plane of the
rolled product that is not parallel to the rolling direction, the sulphide
stringers break the surface as spots (cross-sections of the stringers), and
these spots are particularly susceptible to corrosion." -B. Reynolds

Any comments on this? While I think that the chemistry of the bath is
critical but I have been miffed by the fact that one plate will come out
pitted and another fine in the same bath.

Another point of interest is that there are some many things that can go
wrong that it's sometimes difficult to determine the exact reason. That is
what I need to do however and the stainless grade seems to be the most
plausible so far.