Hi Paul, I think you confused the GTL 10th Anniversary Patch 9.8 (this is the PATCH you should install over full game) and the DEMO 10th Anniversary 1.1 (not a patch) which is only the demo with 3 cars/1 track.
So if you have got lot of mods then move your gamedata folder elsewhere on your hdd, delete your gtl game folder, do a clean install with steam, restore your gamedata folder, install GTL 10th Anniversary Patch v9.8 (the patch for the full game)
small UI update :
- centered round icons on the bottom bar
- updated a bit the showroom
- replaced the 6 custom championships by only 1 custom championship template : you can edit/add other championships as you want anyway, remember to add your new gdb (file full name) to CUPSTAGES.GDB at line 100.