I'm guessing that all those skirts are one piece skirts, i.e. false fronts. In most of the patterns/extant gowns I've seen from the 1870's, especially the early 70's, they do that instead of full over & under skirts on the flat fronted dresses. The upside of course, is you save a lot of fabric that way, plus it's not so heavy.
Good luck on your dress! The world needs more bustle dresses! :)