right! this will clear things up
Firstly the sync method is purely for the remote locking & has nothing to do with the immob or starting the car
Secondly, when you lost your original key it was deleted from the immob when your new key was programmed. When people get a spare key done the the original key has to be programmed again with the new key, any not not done get deleted. You can't just add a new key like you can with other makes such as Ford etc.
Thirdly, even if you have the key tab & you order a key from the dealers it doesn't come pre-programmed to the car. They order the key to details stored with chassis number etc. The blade comes pre-cut but they still have to program the key into the car so it recognises it. The immob chip in the new key is blank until it's programmed regardless of where you get it from