I was surprised I didn't see much discussion about these swings or the effect of cold ambient temperature, because they'd be critical in evaluating a used car for someone in a cold climate. Battery temperatures didn't swing as wildly or seem to have as much of an effect.
I have Leaf Spy running on a spare phone almost all the time and logging to Dropbox. Although these are my max/min readings over a timeframe, none are really outliers from the surrounding data. It seems to take about 3 days for readings to stabilize after a big ambient temperature swing.
I've also seen GIDs at 100% charge swing accordingly from 259 to 284 over the same timeframe, although they seem to max out at 284 for any AHr reading above the high 65 range.
Based on the way the data is trending for my car, I may have a low enough AHr reading by mid summer to lose a bar after showing 103+ Hx at times in the winter! Perhaps if things continue I'll make and publish a trend of the data.