Yes. I used Retroarch. In the Edit Emulator tab under the associated platform Sega CD, Default Command-Line Parameters I left it untouched as -L "cores\genesis_plus_gx_libretro.dll", the Default Emulator box is also checked.
To double check, when I right-click Edit on the game individually, under the Emulation tab, it had also said Retroarch. Sega CD was also spelled correctly in all my folders.
Technically the games did launch on Retroarch. It's just that it launched a black screen that doesn't do anything. If I used Retroarch on its own without Launchbox, the games did open with no problems. If I go back to Launchbox to open the same game, it'd open to the paused screen of the game on Retroarch and it wouldn't load. If I open a new game, it'd be a black screen.
If it helps, I had downloaded Kega Fusion just to check if the files would open on Launchbox and they did. I would leave the associated plaform to Kega Fusion but the screen size was way overstretched and I right clicked to fiddle with the fullscreen & video settings but didn't manage to adjust it to my liking. Anyway, I'd rather just leave it to Retroarch if I can. It works fine for Genesis and SNES but it just doesn't work for Sega CD for some reason.
Thanks again for your help