This is certainly odd....the missed approach waypoint MXxxx
some years ago, there was a movement to code in the missed approach point as a waypoint, so that a pilot could see the distance to the MAP....
while it sounded like a good idea, the logistics of adding and maintaining this many waypoints, negated any benefits.
with the 424 coding, at least all the ones I have coded, the RWxx is required. I did several approach procedures into China where the runways were brand new, and not in any Navdatabase, the FMC would disco if there was not a specific RWxx point.
There was also significant issue on a few of them, as the Smiths box would not accept runways above 10,000 feet, so even creating waypoints with very small offsets didnt work.