That's what I'm trying to understand, the science behind the software update before I have it done.
We don't have access to the details of how the update works. All that we know is this:
* The update resets the BMS to read 12 bars.
* As the BMS relearns the actual capacity, the 12 bars may remain, or one or more of them may once again be lost over the next few weeks and months.
* Some people have regained and retained 12 bars.
* Some people have regained all lost bars and then have re-lost one or more, but not all of them.
* Some people have seen no actual improvement in capacity or range, just the usual effects of a BMS reset.
In my used Leaf buying guide I note that the only 30kwh Leafs that you can count on to have 12 bars of actual capacity are the ones that show 12 bars with no update.
* I'm going to add here that I believe that a 30kwh Leaf showing three or more lost bars is very likely NOT a 12 bar car with a software error. An 11 bar 30kwh Leaf may (or may not) just have faulty BMS programming. Nissan claims that the 30kwh packs degrade at the same rate as the 24kwh 2015 "Lizard" packs, but the reality seems to be that degradation is a mixed bag with these packs, with some of them degrading fairly rapidly and some retaining capacity well. The latter seem to mainly in cooler climates. I have dubbed them "Lettuce Packs" because they seem to wilt (lose bars) in the heat and stay "fresh" in cool temps.
* You can also determine actual capacity by doing a range test that involves driving the car X miles and then extrapolating to a full charge to Very Low Battery Warning or empty drive, or by doing a full charge from near empty and measuring the number of kilowatt hours added.