05-08-2016 12:23
05-08-2016 12:23
05-08-2016 12:45
05-08-2016 12:45
I don't think I can answer all the points you raise but I think you may not be aware of the way fitbits track BMR calories.
As well as tracking calories you burn through activity, your fitbit also tracks your BMR calories. These are the calories you burn just keeping your body alive (even when asleep). They are calculated from your profile settings (age, weight etc) so you needn't be wearing your fitbit to get them. What you are seeing on those days you didn't wear your fitbit is the total BMR calories for the day. There's more information on this here:
05-08-2016 13:59
05-08-2016 13:59