Nor is it an excuse they use. It is the reason that the
global collapse model had simplified geometry.
The model you mention is the initial partial LS-DYNA model that was used to establish failure modes and criteria for the ANSYS model. As you know this model WAS a lot more detailed.
It omitted the web/flange stiffener plate, however in this simulation failure of the flange was not actually observed as the result of the simulation was the girder being "rocked" off its seat. So in this instance the presence of that stiffener would not have seemed to have made a difference.
And based on this rendering, they correctly modelled the seat at 12" in this model.