mutt, you say:
So I suggest that as there is NO procedure that allows you to use the 10 kts tailwind data for zero wind conditions, you don’t do it!
Practically, I would beg to differ. Many places I fly to (Africa & Caribbean for starters) often give quite misleading weather data. I can cope with temperature because I have an accurate reading on the screen in front of me but they haven't yet fitted the 777 with an ground-reading anemometer.
If Abuja tower are giving 'light and variable', I use 10kts tail in the calculations as a 'worst case' (probably not enough, actually!), based on the reasoning that that I will get a better safety margin. I have thought long and hard and fail to see any case where you will get
worse performance out of the aircraft if you don't get as much tailwind as you planned. A lack of accredited headwind, yes but tailwind, surely not..?