hi Samraku,
i think i had the same questions, as terms were confusing,
ABOK #545 is a 3-lead x 4-bight single strand stopper knot,
and it originates from a ring mat
ABOK#599 is called a ‘single-strand’ button,
and i think that’s where the confusion lies, because yes it’s tied from a single strand, but it has two ends.