I'm having trouble with a 19 mile shift, of several benchmarks, over a relatively brief period of time. 19 miles, 19 months, 19 passes...
A mile a month seems a lot of floating around in a short time.
I also have trouble with an internal ocean with stable core and floating shell;
I'm picuring one of those toy balls that never bounce he same way twice...or,
Testing a hard boiled egg by spining it on the counter - if it wobles, it's not cooked.
What are he chances that they just screwed up their measurements?
And, if it actually does occur, do I assume the shifts are either in the same direction as spin or orbit, against either one, some discernible tangent caused by both, or random?
Things are drifting around with relative motions. Some things have moved 19 mles, some haven't. They might also be taking gravimetric measurements of the body of the moon for comparison. The measurements are fairly tight by the nature of the instruments.