It's interesting to study old parts catalogues.
Amongst their other movements, Minerva pocketwatches had a half dozen basic "movements" that shared all parts EXCEPT bridges, regulator and certain screws. There was an entire family of 17''' movements based on a common set of wheels, barrel etc, and a set of 19''' movements. And they were even available in American sizes to be cased in the US. So, something like six basic sets of components were "dressed up" in about two dozen different calibres. Add in very different levels of finish, different regulators (snail, swan's neck...) , different qualities of jewels, different balances (split, solid, pretend split) and you've got a wonderful matrix of possibilities. I have a couple fo example where the base plate has spare holes that are probably for mounting other combinations of bridges.
nick