It's a good idea to standardize a status code to do so if the specific case is often going to affect clients' interpretation of the response, and it's a widely relevant distinction, so there are many other services who hit equivalent cases and would use the status codes to differentiate them. Even if these errors do happen widely, do we really need a separate HTTP status code for hosted logic errors and platform errors? Platforms just need to watch their monitoring for 555 errors, and developers & API clients can know that 555 errors are always caused by the service's platform, not the service itself, so everything except 555 is semantically related to the service.