When constructing a diminished seventh, the ‘seven’ is double-flatted. This continues the series of minor third intervals. So Cdim7 is C, Eb, Gb, A. The A is Bbb enharmonically. No, that’s not a typo. Thus there are only three diminished seventh chords before the pattern repeats.

Some years ago when we discussed all this, I believe that it makes a difference what style you are using, whether BIAB will play that double-flatted seventh.

If I recall correctly, either in Preferences Arrange or maybe Display Options, you get a chance to specify how you want this chord to look.

BIAB 2024 Win Audiophile. Software: Studio One 6.5 Pro, Swam horns, Acoustica-7, Notion 6; Win 11 Home. Hardware: Intel i9, 32 Gb; Roland Integra-7, Presonus Studio 192, Presonus Faderport 8, Royer 121, Adam Sub8 & A5X monitors