Very little aside from the fact they worked with Boeing to make the calculation adjustments.

My highly uneducated guess from what I remember of physics/engineering, and the minimal amounts of W&B knowledge I've gleaned from [MENTION=10236]LarryJ[/MENTION] posting here that W&B is done by breaking the plane into zones and the issue on the 757 with seat blocking being concerns over floor load limits within certain sections, is that they were able to adjust how those zones were defined which allowed the calculations to show the load limit for the floor within the zone wasn't being exceeded.