Most jet fuel is still kerosene based...

Based is a key word there.

Gavin a quick google search will give you the grades of steel used in the Twin Towers. The NYC Department of Buildings keeps and kept decent records on all buildings. Investigators were able to find the impact steel of both towers because of Department of Building records of the buildings. For governmentallly funded buildings records are extremely meticulous.

It is highly unlikely the grade was consitant, corruption runs deep with these things, usally only certain areas actaully meet the code, and a lot of areas are completely random, even if you try to meet code it is highly likely your suppliers with these beams is inconsitant, its just the way this stuff works.

(Sources, my family does this **** for a living)