You will have noted that generally REC MAX alt in an A320 is FL391, to allow for +/- 50' variations in the cruise but some have a REC MAX of FL394 and some have FL398! Go figure?
Hi charlies angel,
it is a matter of certification actually, having the airplane certified up to FL398 is quite useful in metric operations where you can accept some higher levels in meters. I guess this has been done to promotes airplane sales in countries operating with metric reference.
Cheers.