Tim, sorry, what are you saying is the final metric they're using to calculate 70% (or maybe less than 70%)? Does anyone know? Or is this purely empirical, where people can observe "no one who had a Ahr reading above x ever got a battery warranty replacement"? Seems like it should be based on kWh measurements, not "bar programming". As another friend who is a leaf owner liked to point out, "if we can't trust VW on emissions control programming, should we trust Nissan on battery bar programming?"
Seems like you've got it pretty well figured out: No, nobody knows exactly how Nissan's software determines when the bars drop, and I'm sure Nissan would guard this algorithm as a "trade secret" protected by the DMCA, which means it'd be ILLEGAL for any of us to even try to extract the code from our cars!
Worse, even though Nissan has said
that its mandatory software updates (such as the infamous P3227 update) won't affect the bar loss thresholds, no one has been able to independently verify this. And unfortunately the VW lesson is clear that their software SHOULD be independently verified.
What we do know is that it's quite clear that bar loss happens well after the drop below 70% capacity, according to the only ways we have of measuring capacity (i.e. LeafSpy or other CAN readers.) I'm at 65% and still waiting for that bar to drop.
Another way to measure your capacity loss (without LeafSpy) that I've suggested is to perform one or more "range tests": Reset your trip odometer and trip efficiency meter after a 100% charge, then drive all the way down as low as possible. You can return home after VLBW but I'd recommend then leaving the car on and using as much power as possible (running the defroster could help) until the car eventually hits turtle then HV disconnect. Make sure you're around when this happens, as the car will quickly drain the 12V battery after HV disconnect and you could be left needing a jump and/or damaging your 12V.
After HV disconnect, take a picture of your dash to note the miles driven and miles/kWh achieved, and divide to determine your available capacity. That number divided by the 21.5 usable capacity when new is the best way I know of to measure your capacity loss outside of LeafSpy (and I've found they do agree very well.) The reason I suggest doing this is it uses only Nissan's own instrumentation and no 3rd party devices of any kind.
Your suggestion that you'll open a case with Nissan is a very good one: History has shown
that the "squeaky wheel gets the grease", as Nissan has been known to grant a few outside-of-warranty replacements to those who made a stink about it. Bring the car in complaining of range, and if you can document that with a range test like I described it couldn't hurt. But I'd expect anyone from Nissan to completely ignore any LeafSpy readings as a matter of policy.