This question has a fundamental misunderstanding of money supply and the link with coinbase transactions.

You would be right in a perfectly secure system, the coinbase transactions are the only way to add coins to the money supply.

The reality however is different. Bugs in the protocol (like the infamous keyimage bug that allowed the creation of infinite money) can create additional coins in the system.

Creating commands like print_coinbase_tx_sum may give you a good indication of the money supply but it should not be taken for facts.