There us no such thing as immutable data. The only constant is change. I'm suggesting that in the modeling of the data structures in a system, you rely only on

There us no such thing as immutable data. The only constant is change. I'm suggesting that in the modeling of the data structures in a system, you rely only on the surrogate value and not the actual values. You're holding an immutable key to mutable data, that can be altered, but isn't necessary to be constant for the system to work. There is really no alternative, because laws are making it increasingly likely that immutable data stores will not be legally sound. Data stores like datomic have the notion of excision to handle this. Blockchains may require immutability, but that simply means you shouldn't put data in that must be removed by a court order.