@ibaird Not 100% sure on this but Notarcha aurolinealis has a white fascia between the black discal spot and the last black spot on the costa; not present in Notarcha obrinusalis as in my specimen. Are there other ways to distinguish these species?
Sorry, I am not familiar with these species, but looking at both moths online they are hard to distinguish just on the criterion you have identified given the amount of variation evident. But I reckon A. aurolinialis I think might br a better ID given I thought there were a few identified which lacked the white 'fascia' (if I'm interpreting your words correctly).
@ibaird In my specimen and all but one (rather washed out) example on BOLD, of Notarcha obrinusalis, the 'outer' (at 2/3rds) black spot on the forewing costa sits right on a dark orange band. In comparison this black spot in Notarcha aurolinealis slightly offset towards the thorax, and sits above a white patch which is lacking in my specimen and other examples of Notarcha obrinusalis on BOLD.