Here is my latest thought on the quarterly adjustments. Safe Harbor warning, no science or methodology sits behinds this hypothesis.
My guess is that Nissan is quarterly tuning the amount of buffer, and with it bringing down the SoH reported to reduce the speed of degradation of the battery. In doing so, the battery post tuning is under reporting true remaining SoH. Then as the battery ages, if the battery underneath stays flatter, it can give back a little of the capacity in line with their internal model. In this way, it can help de-risk its potential battery replacements (under the 8 year / 70% warranty...same as Tesla) as well as help consumers maintain the best battery possible given their usage habits. Almost like how Tesla will throttle back supercharing on cars if its done too much to protect the brand, this is Nissan's way of doing it.
All anecdotal. We are coming up on the 1 year anniversary of our car, and it is doing well. Battery is at 95.67% and I should know in a few days if that is pre or post the last adjustment.
2019 S Plus (98.6% SOH) & 2019 SV Plus (94.6% SOH) Both Silver
2013 Leaf SV sold 2019
100 Mile Club Member (Number 87)
Max Miles on 13 Leaf: 120 miles
Max Miles on 19 SV Leaf: 242 Highway 4.5 miles/kWh