This is true for many things but not for consensus systems.

In a consensus system with multiple major implementations if _any_ implementation has an issue everyone has an issue-- and if there is just a "disagreement" but none are objectively wrong, then there is still an issue.

The reason for this is that for a consensus system the primary purpose is to be consistent, so any inconsistency is a failure, regardless of whom is "right" vs "wrong" or even an otherwise harmless difference.  Inconsistency immediately creates an opportunity for funds theft, when you think a state is final but it really isn't and it gets reversed.

An implementation is a _precise_ definition.  A pile of paper is not, or to the extent that it is precise it's still not that relevant: if paper says X and the network does Y, then Y it is, you can't generally just undo Y later without undoing transactions that people thought were final and irreversible.  Good specs are useful to aid understanding and analysis, but cannot define the network because they cannot control its action from moment to moment.

The implications are clear to anyone who has spent a reasonable amount of time doing serious engineering for a distributed consensus system.