>it would even simplify tagging for signals in countries where different >heights at the same pole are permitted
It also allows to simplify initial mapping of signal - you don't need to know exact type of signal in order to add its height to OSM (for example, if you've seen it from backward only). >If all of these 4 signals are identical, i.e. a every combination of lights on >any of them has the same meaning on all others That's right, all of them (and today I've seen the 5th variant YXY-XWR - https://ibb.co/0hCwZL5 ) are intermediate/exit signals with the same meaning of any state.
