In North America, 2003-2007 Cadillac CTS sedans used a 4-button keyfob with FCC ID L2C0005T on the back. This vehicle had seat memory as standard equipment, so the original keyfobs had fob numbers 1 and 2 on the back. These numbers are purely cosmetic; they are there to help the user distinguish one from the other but they have no effect on functionality. When buy a replacement car remote for these Cadillac CTS models, you can buy either seat memory remote and it will work with your system regardless of what other keyfobs you use with the vehicle.
These applications require dealership programming with a scan tool.