A skim of various Google results (e.g. How to tell if my mitutoyo calipers are fake? and Is it an original mitutoyo vernier caliper?) followed by a quick visual inspection of my purchase leads me to believe that I’m the proud new owner of a pair of authentic Mitutoyo 500-196-30 AOS Digimatic Calipers. They were a few bucks cheaper from a trustworthy-seeming Taobao seller than they were on Amazon.
My old no-name calipers with their slightly non-parallel jaws have been consigned to the purgatory-for-unreliable-tools drawer, where they will await an unspecified, hypothetical future need for crappy digital calipers or, more likely, disposal.