Itinerant1, your Li batts are obviously doing well the way you do things.
From the link Phil posted:
"If you’ve held onto a phone for a year or more, you’ve probably noticed the battery doesn’t seem to last as long as it did when it was brand new. Two years down the line and many phones struggle to make it through the day on a single charge. Holding onto a phone past three years can even spell trouble for system stability.
Unfortunately, battery capacity inevitably declines with age."
So "lasting as long" is the same as not taking as many AH as before to get down to 50% from 90% and the same idea for number of AH to recharge from 50-90.
Wets sulphate to cause that. Don't know what happens with Li to "age" them. Stressing with too high voltage for too long was mentioned as a factor.
Charging efficiency while recharging does affect the accuracy of a battery monitor. Trimetric (Bogart) has put out the number for Li to use with its monitor instead of the default value. I suppose your method allows for that, or else you stop charging soon enough that it doesn't become critical.