Ever notice that everything they find is always never seen? Well that's silly. In fact part of this discovery came from "seeing" shifts in the surface topography of Titan in the short time that Cassini has been orbiting Saturn.
They found sulfur volcanoes on Jupiter's moon Io, through visual observations.
They found fractured ice all over the surface of Europa, that was seen.
They found active stream gullies on Mars and ancient riverbeds by seeing them.
They found an asteroid with it's own little moon by seeing it.
They even saw a comet crash into Jupiter which left us with a whole host of new science to chew on.
Science is about discovery both visual and inferred from observation and calculation.
You seem prepared, and I'm a liberal arts major:
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?