“If a system is maintained over an extended period and has observed behavioral traits that are consistent within that period, that is, in itself, strong evidence that those behavioral traits are consistent with the purpose for which the system is permitted to exist” is kind of a mouthful, though, and there is value in succinctness.

(Although there is another message, there, too: “the purpose of a system, insofar as it can be said to exist separate from what it actually does, has no weight in justifying the system’s existence or design”.)