Long thread so I’m probably repeating the above, but the issue is what does it mean? 8 by itself is clear when positioned above or below. 8va obviously is a widely understood abbreviation for ottava. 8ba is an abbreviation for ottava bassa. What’s 8vb even mean? Ottava bassa? That’s really odd as an abbreviation.
Virtually no style guides allow for that as an abbreviation. As one more, here’s what Kurt Stone has to say about it:
