Some of the STY files are substyles files (part markers C/D, E/F, etc) which aren't listed in StylePicker as standalone styles, so StylePicker will always have fewer entries than the number of STY files.

My computer has 10,028 STY files in the BB\Styles folder. StylePicker shows 9,690, leaving 338 unaccounted for. Of those, there are 154 substyles files (they're the ones that end in a "+" in the filename. That leaves 184 not accounted for. I have a bunch I've downloaded from the web over the years,so it is possible some of them might be corrupt or unreadable.

Laptop-HP Omen I7-10750H Win10Pro 32GB 2x1TB SSD/2TB SATA
Desktop-ASUS-I7-3770 Win10Pro 32GB 2x2TB SATA

BB2021/UMC404HD/Casios/Cakewalk/Reaper/Studio One/MixBus/Notion/Finale/Dorico/Noteworthy/NI/Halion/IK