Would you play different notes for add2 vs add9, or would it depend more on context than how it's notated?
if you can prove that the transcriptionist commonly uses both symbols, then indeed you can assume that the octave matters, because they would have used the other one if they meant the other one. but if they seem to always use the same one, then i'd say there's no way of knowing which octave they'd prefer for you to put that note