I doubt the radio will be different, I can think of no reason why the Rover radio should have different firmware in it to a BMW radio, apart from the age of the radio (given that development of Rover units stopped when BMW sold Rover to Ford)

So a BMW radio will have newer firmware than Rover.

eg: if you want to use a BM24, use one with software version v9.0 or later (I have v10.0) for full compatibility with the Mk4 nav. Earlier versions work but produce undesirable effects at times, like switching to the radio screen for no apparent reason!