You are sooo right,…Not about chords not being in the list, because all possible chords are in the list. (Save, maybe some chords only used by Debussy or Dave Liebman) But…
Today, midi styles play only 7 different chord types (for the bass, that is, for piano, maybe 10). For the real styles it’s sometimes better, sometimes worse.
My way of describing it.
Band in a box can DISPLAY all chord types, but can only PLAY the basic chord types, largely ignoring alterations or playing them wrongly.

Of course, the algorithm tries to enhance or embellish. Cause most people just write chords that don’t define the proper harmony. They write C7, where C7#11 is required. It’s a trade-off.
As users, we should write the chords properly and pgmusic should have their algorithm fixed so chords are played correctly. If they fixed that, you would be happier. Me too.