In two recent issues of Down Beat (December 2011 & June 2013). There are articles on “poly chords”.

Two chords stacked one upon the other, e.g. Cmaj7 plus Dmaj7.
This can be written as Cmaj7/Dmaj7, however not in BB as the slash is used to indicate a desired bass note (e.g. Am7/G).

Of course if one spells out the notes of Cmaj7/ Dmaj7: C, E, G, B, D, F#, A and C# one could use the tertian terms (for the Dmaj7 chord tones): 9, #11, 13, #15. This has however some unlucky consequences in BB, as #11 will alter the G in the C-chord and #15 is not recognized.

Has anyone a suggestion that will work around these two problems?
Please let me hear from you.

Tonnie