One Key for two cars.
The 2004,2005 FOB is programmed in two steps.
First the immobilizer is programmed. This allows the car to start and run.
Second, it is programmed to unlock, and lock the doors. This function involves the key code. Two cars will not have the same key code.
Conclusion: One Key for two cars? Yes, for starting and running.
No, for locking and unlocking doors.
If you purchase a used FOB, forget even the dealer to program the door locks. The key code is only programmed once.
The above info came by trial and error on my part.