Ha, Music Student, thx a lot!
I believe I cracked the code,

but the bass still doesn’t play any sophisticated chords. The weird thing is that some styles play correct piano parts. So there is an algorithm that is limited to piano and guitar and that is invisible and only works in some styles. And there is no credible reason why they shouldn’t use it for the bass.
Happily, modern jazz bass players play more groove oriented (Dave Holland and Christian McBride especially), so they favor fifths and sevenths. And to prevent strange bass mistakes,
i also “simplify” the bass lines favoring groove over harmony, sadly, but it works and sounds really good.And, I notate a lot of stuff as slash chords.C Diminished, I notate as B/C (B triad, C in the bass)
C Phrygian as Db/C: Db triad over C bass note.
A/C for C13b9
E/C for Cmajaugmented
Slash chords produce correct notes, but not always the best note choice. Biab has a funny way of playing slash chords, sometimes good, sometimes not so good. So, you don’t get wrong notes, but not always the most tasteful ones.
Anyways it’s still the best I could come up with and
works nicely. Yamaha and Roland know a lot of chords, but not the modern ones, like slash chords and phrygian-sus chords. The chords of the Levine Jazz piano book or Jazz harmony book.
To be honest,
it took me more than two years to come up with usable styles. The whole process, even if I only have bass and drums and just a little piano, is really complex. But after two years I suddenly managed to make some good styles and now a year later I have a lot of great ones. Still, If you have some ballad, some modal... styles, you can cover a lot of ground. I must have 200+ good styles, but most tunes are covered by some thirty or forty styles. To keep it intresting
I never recycle bass or drum parts. Every single style is made from a different Midi file. And though some styles may have a similar feel, they are always different and that prevents boredom.
The way I tried it at first, just trying to come up with nice grooves, doesn’t work. After a while I started with a good song (Jarrett, Joshua Redman, Calderazzo, Branford Marsalis, Jan Garbarek, Kenny Wheeler). I
kind of copied drum and bass parts and then translated them to 2 chords per bar, 4 per bar, 1 chord per two bars... (just simplifying here). It takes about 8 hours to make a midi and make it into a style. And then some 8 hours to tweak it properly, to add information, to get the piano chords right, to correct all little mistakes and so on. Mind you, I’ve been at it for some years now and even took some unpaid leave to make styles.
Mind you, these styles are not run of the mill, Yamaha-style party-jazz. They are
quite spicy and they inspire me, but maybe for others they don’t work.
Thx for your encouragement.