There might be more
From The Lost Media Wiki
In "Garfield takes his licks" a page has "Top Ten Comic Strips Jim Davis Tried Before Garfield". While we don't know how far these got or if they're real, they're worth noting. 10. Andy Amoeba 9. The Domestic squabblers 8. Randy Rash 7. Crazy Crayfish 6. Sid the Sperm Whale 5. J.M. Keynes, Kid Economist 4. Billy the Bagman 3. Milt the Incontinent Hamster 2. Gnorm Gnat 1. Garfield the Toaster