The version is not auto-detected in USBLoaderGX, instead it's using a list of known release date and link it to known version number.
So, on the current latest version of USBLoaderGX (r1211), the latest known DIOS MIOS version is 2.8
If you install DM2.9, the credit page of the loader will only display "2.8+", as it doesn't know 2.9 release date yet.
It's the same with syscheck and all other loaders based on DM release date instead of the internal MIOS version number.
The internal MIOS version was not always correct in the past, that's why we are using hard coded release dates instead. It require some updates of the homebrew dependent on DM version, but there's not a lot of release every week so it's not that hard to keep it updated manually.