It seems to be coming down to how you define "identifier".
Technically everything in the blockchain has a unique identifier because transactions are unique (hash collision is not possible specially after BIP-34) and the block containing those transactions and even the order of transactions in that block are unique.

So the 50 BTC reward of a block in your example is the reward inside a transaction with a unique hash with unique UTXO(s) that is also included in a block with a unique hash which is part of the chain at a certain height.
All of these "identifiers" make those coins unique.