Instead of carrying all those specialty oils, the OP could just go all Mobil.
Mobil 1 0W-20, 0W-30, 5W-20, and 5w30 for American and Japanese cars.
Mobil Super 5000 in 5W-20 and 5w30 for conventional oil changes.
Mobil 1 5W-40 European Car Formula for European cars.
Mobil 1 5W-40 Turbo Diesel Truck for HD diesel engines.
Mobil 1 ESP 0W-30, 5w30, and 5W-40 for diesel cars(European and American).
These oils would probably do 99% of the vehicles that the OP services. If the OP does not do very many diesel cars and trucks then they can omit the diesel oils.