I checked and found that a lot of my personal styles show something other than "User" as the set number.
If you are making variations of newer styles - in other words, you made a copy of an existing style that was made by PG Music within the last couple years, then Band-in-a-Box is probably picking up the 'Style memo' data embedded in the style. You could open the StyleMaker - ctrl+shift+f9, click MISC -> Style Memos etc. If the extra settings are enabled, you can set the "Styles disk #" to 999. After a slow rebuild, this style should show up as a User Style.
5/07/2020
Does that explain something about the problem?
No, I'm not quite sure what the cause of the problem is. This is the correct date (05/07/2020, or later). If you Fast Rebuild (slow rebuild not necessary) after installing Xtra Styles PAK 9, you should definitely see them in the StylePicker.
Even if you install the Xtra Styles PAK 9? I'm sure you have, I just can't think of a reason why you would have a Feb. file.
The only difference is that slow rebuild looks for 'user' (non-PG Music) styles. Perhaps we could state that right in the menu option to make it clear.