Do I recall correctly that Usener wrote in German? I presume that now given our internet reach we have the ability to ask Martin and possibly others as well for assistance in understanding Usener's own notes on these issues?
Or are you already able to consult Usener?
He actually wrote in Latin:
Hermann Usener Epicurea ( 1887) : Hermann Usener (editor) : Free Download, Borrow, and Streaming : Internet Archive
Epicurea is a collection of texts, fragments and testimonies by Epicurus composed by Hermann Usener in 1887
archive.org
I've been using Bailey and Usener interchangeably since I think Bailey was a protege of his?