> My sense is that you would have to be a very practiced (that is, consistent) baker to notice the difference imparted by the possibility culture in your own bread.

The difference that San Francisco lactic bacteria impart on bread flavoring is obvious and pronounced. It does not take an expert or particularly trained taster to taste. It is a literal mutant strain of the bacteria.

I do agree, however, that this statement is probably true of other regional varieties of naturally leavened breads. Assuming everything else is equal.