The 78/79 numbers are imaginary. They're the result of incomplete calibration to the real pack, combined with the fudge data in the 3 BMS. The "rapid degradation" at first isn't degradation at all.
(To be clear, the reasoning behind why the CAN-reported values don't match reality may not be, and likely isn't, nefarious... my guess, based on what I can tell from my RE work, is that they just didn't care if those values were accurate since they weren't used by the vehicle... internally, there are more accurate values that aren't reported on CAN and require active polling to retrieve.)
So if the original numbers are over-zealous, does that mean the CANbus numbers can be trusted after the electrons settle down? Say, after 5k, 10k, 20k, etc. miles?
The reason I ask, is because on a 90D, I can charge to 100% and then taking "Usable Full" from the CANbus, divided by EPA wpm of 290 (.290), go *exactly* that amount of miles in one stretch and have the dash read 0 at the end by keeping consumption at that 290 number for the whole trip.
Now, at 100%, the car (dashboard) overstates range by the 4kw difference in Nominal and Usable so I'll never get that rated number at the 290wpm consumption, but at least I'm aware of that.