Lots of comments about phantom fuel.
Maybe it's time to think not in terms of phantom fuel but fuel that exists due to A/B/C, e.g. due leaking seals etc, but subsequently is actually used as per design using the scavenge pumps.
Unexplained fuel in a centre tank does not mean phantom fuel which implies that it does not exist.
There may be a perfect reason for those tanks to indicate fuel, as explained for various technical reasons, the amount of fuel of which can be indicating a different amount at varying stages of flight due pitch attitude, acceleration/deceleration, turns and subsequent time required to settle again for accurate measuring.