Eventually tissue samples might be analyzed for genetic markers that would establish the relatedness of the Kona and Hilo birds.  Until then, it seems best to provisionally maintain the subspecies status as a marker of their indeterminate differentness—and to use the names “Rusty” and “Dusky” to clearly denote their principal differences.

Upon their original descriptions to science, the Kona birds were classified as sandwichensis and the later-described Hilo birds as a separate species, millsi.  In the ensuing decades when Hawaiian bird taxonomy was a contentious field, the Kona and Hilo birds were either considered separate species or divergent subspecies.

Nobody knew then whether the two groups had descended from the same initial colonization event—in fact, the theory of evolution was not yet widely understood.  If they were known now to have resulted from different colonizations, most taxonomists would automatically regard them as separate species, whereas if both arose from a common colonist their species status would require further analysis.

Since the mid-1900s, however, the prevailing view has been that the two Kona birds are both immatures and the five Hilo birds are all adults, and that the apparent regional difference is just a coincidental sampling artifact.  The theoretical underpinning of this view is that one island would be unlikely to support two similar species of small flightless rail—because that type of niche on a single island would rarely be capacious enough for two species to occupy it.