Just need to double check before I drop 300 to program a new key--- if a key unlocks and locks a door-- that means the Nissan BCM properly read the code the key transmitted right? Intelligent Key and BCM Troubleshooting

Is there some other different part of the key that receives a signal from the car for ignition/start-button? Even if the receiver of the key itself has no power since I held the key by the start button and inside the receptacle, which should work even with a dead battery, and given that the key code programming is correct since it unlocked the door.

The other case I can think of is if the receiver of the key is broken, then it can still transmit to unlock, but can't recieve the ping from the car to trigger the ignition with a code- is that the right understanding?