Perhaps the standard bandoneon symbol indicates L paired with the in-tune M; while the bandoneon-with-mark indicates L paired with the sharp-M?Thanks for sharing the above pictures, Glug?
So what do we have?
Bandoneon reed only in cassotto.
But, only one coupler displays the bandoneon marking and both have the mysterious, other symbol.
So, the mystery symbol shouldn't relate to cassotto?
Also, each right hand coupler already has a twin, except for also having the mystery mark.
And, the mystery mark changes location from coupler to coupler.
So what's different between having the mystery mark and not having it??
Beats me?