To wilyflier #926:
The AAIB special bulletin 1/2008 does not mention any recollection of the crew switching the crossfeed valves or finding one of them open or partially open.
Quoting 1/2008, page 2:
"The total fuel on board was indicating 10,500 kg, which was distributed almost equally between the left and right main fuel tanks, with a minor imbalance of about 300 kg. The crossfeed valves indicated that they were closed and they had not been operated during the flight."
This implies the AAIB has been able to confirm this from the FDR data (and likely from crew interviews) or they would not have made the statement: ". . .and they had not been operated during the flight."
Those are the officially published facts sofar regarding the crossfeed valves. No more, no less.
In light of only 300 kg imbalance between left and right main tank, it is also ruled out that one of the crossfeed valves could have been (partially) open undetected.
Green-dot