Just to answer your question. Take your current AHr rating and divide it by your current SOH rating, and that'll get you the original AHr rating when new: 64.77 / 0.81 = 79.96 AHr
Others have lost their 4th bar at something above 40AHr, so you shouldn't have to wait too long.
On another front, since your battery is degrading so quickly, you might as well use it without regards to preserving battery life. You might get your warranty replacement sooner, and you might be surprised at what does or does not impact the battery health!
Yes, that is my plan. Ironically, I took it into the dealer on Friday and had the battery report done. He said "the battery looks good...in fact it is excellent!". It was on my way home from the dealer that I noticed the 12th bar was missing.
Nissan - Redefining Excellence!