I believe they know the stress that the West corner of the sliding & partially rotating sidewall & slab have sustained and/or are under. A conservative estimate of the downslope shift is from 3 inches to 5 inches judging from the repaired sidewall and spillway gaps.
Now translate that movement into the combined retention force against 16 to 20 anchor bars of #11 steel (1.41" dia) rebar emplaced within NX grouted holes (2.15" dia) drilled into 5 feet of sound rock (or what the blueprints state as determined to be "sound rock").
I'm intentionally discounting the large number of anchor bars in the sidewall itself as there was notable sign of potential of subsurface compromising of these anchors via erosion.
IF the slab anchor bars experienced a "bend" from the downslope movement, there should be a slight shift of the slab height (minor drop). However, the photos did not indicate a slab height shift (best estimate of zoom). If not a "bending" force, then the shift occurred from either a pulling of the anchor bar(s) out of their emplacement -OR- a fracturing of the concrete within the slab around the anchor bars -OR- a structural integrity loss of the "sound rock" around all/most of the anchor bars.
In any case, the forces are significant. No surprise they bolted on a precision optical movement detection target on the shifted sidewall.
I think that the entire remaining spillway parts have been severely damaged. The “West corner” appears to have shifted significantly as you observe. As far as the bolts being driven into the floor, did anyone see a drill rig out in that area(?) or was it just some guys with hand held units. If it was a human held drill process then they are way undersized and probably not deep enough for them to remain anchored for a significant period. I also think they are kidding themselves with the sealant work. Getting good adhesion on concrete even with modern day sealants is tricky at best. The forces involved with that water flow are immense and the sealants are bound to fail sooner rather than later.
The discharge rate of the water at the drain outlets seems to be increasing as time passes. At some flow rate it will do more damage to the supporting ground under the spillway and another breach in the floor will appear.