A film has only one ISO speed based on a set of strict criteria. If this film is ISO 400, that is its speed under ISO test conditions. However once you depart from those conditions, the effective working speed, usually defined as Exposure Index (EI), may or may not change. Some of the factors are objective (perhaps Rodinal does not yield full ISO speed), and others are subjective.

Here is a good summary from Kodak. It will apply to any film.