I think this conflates requirements and implementation choices. "we're never gonna have more than three devices" is a statement about requirements, and implies the absence of a requirement to support more than 3 devices. It does not imply a requirement to fail to support more than 3 devices though, and leaves an implementation choice how many devices to support, as long as it's at least 3.
On the implementation side, the "0, 1, n" rules already mentioned by muxator dictates that this specific aspect of the implementation should not treat 3 different from 5, and implement support for n devices. (By "This specific aspect" I mean that other factors will surely prevent supporting n = 1 trillion, but we don't have to care about that since it doesn't contradict the requirements).
On the implementation side, the "0, 1, n" rules already mentioned by muxator dictates that this specific aspect of the implementation should not treat 3 different from 5, and implement support for n devices. (By "This specific aspect" I mean that other factors will surely prevent supporting n = 1 trillion, but we don't have to care about that since it doesn't contradict the requirements).