I'm not really following this thread, but the title keeps popping up. As is normal, when I lay me down to sleep, my mind goes "left turn Clyde!" And thus it did last night...
I would imagine that we have the moon's orbit and data about it dialed in to the MM. Computers can easily calculate the orbit of the moon down to a knat's a$$. Observed variations from the calculated seen by observation, taking into consideration all of the known influences of known celestial bodies etc., wouldn't those variation provide an indication of an "unknown" celestial body? If not, it may be that we don't have a long enough train of data for it to show. Who knows.... Either way, an interesting topic...