While I understand that various features of pottery may be one of many characteristics useful in helping distinguish different periods and cultures, I think that archeologists put far more weight on this than it merits.
Do we really think that a craftsman who spends much of a lifetime making pottery of only making them in only one style? Not once in an entire lifetime do they get curious about making the pot a little broader at the base or with a different kind of handle? Don’t they ever hear in talks with other craftsmen that 50 miles to the north they put a big swirl on the side, or that a hundred years ago they used to flatten out one section? Really?
Fashion played less role than it does now, where everything else is at best second place — basically, the “if it ain’t broke” rule. The fact that pottery styles are so narrowly restricted in time says to me that the workshop that produced each type was run by the same type-A person for much of its successful run. Like other clay-based products (bricks for example), supply of the raw material would run out at a given spot, making a new style catch on. Variations within a style probably indicate to some extent which employee made it. I think there have been attempts to match fingerprints in the clay. Obviously wider use of thermoluminescence would be nice, hopefully refinements to that method will lead to more testing. Meanwhile the use of unremarkable pottery shards in strata (Egypt, for example) would seem like a good idea.
You have asked an excellent question...