I have 4 devices on same Apple ID. Latest things are there on the iPhone I use. It has about 3500 contacts. For some reason the other devices have less and not-updated contact list. How do I ensure that when I backup on icloud, the latest 3500 contacts of my iPhone are the only ones which get updated across all 4 devices. Also, is there a possibility I lose my contacts on the iPhone during backup if icloud updates from some other device?