Well, it did work at the end, although with some trouble in the middle... to be more clear, I created the custom map file with only "Disk 1" of those games, and removed previous list of files to ignore in Wizard, and the menu in GameEx became nice again without any duplicates.
Then I proceeded to delete some games directly from the GameEx menu, and here the problem appeared again (so once again duplicate titles, as soon as I started to delete some games with the delete key), but fortunately now with the custom map in place, all those duplicate disappear after re-starting GameEx. Previously instead the duplicates remained even after restarting!
I also immediately noticed that if I started to delete games from the bottom of the list (instead of from the top) and then proceed upwards, duplicates would not appear, but as soon as I deleted a second game in the downward direction, a duplicate appeared!
I don't know if this makes any sense But as I said at least now these duplicates disappear when I restart GameEx, so everything is fine. Thanks a lot!! Next week after the party, I'll definitely update GameEx to the latest version