Page 18 of the prelim report references this situation. AF447 had a FCMS (Fuel Management System) that used a 'trim tank' to move CofG aft for cruise. This transfer begins in climb, and, as noted, keep target CofG within 0.5% of target MAC. 37.8% was the estimated aft CofG for this segment of the flight, and actual regulatory aft limit would have been 'behind' that.