OK, now, I get it!
I have really a lot of demos which are not directly available within the style picker... They are all "misc" and with the first sign -

So I solve this with different medicine according to the case:

1) I find the file (-...) within the styles demos (?) and transport it to the drums demos.

2) I load the song file without the first - (that is without the RDrums) and add a RDrum before saving the file under the RDrums-demos, taking care that the demo name is the same as the style name.

A lot of work, but as explained, I love starting from an old midi (MGU) file and progressively change it by adding RTs or HQ instruments....
Bernard