question about the core columns

in the videos of the collpase you can see some of the core columns still standing, 40 and 60 stories in each tower, before they fell 15-25 seconds later.

what do you think is the explanation for that? to me that actually goes in hand with the whole gravitational collapse theory, because the core columns woul dhave been standing if there was a pancake/crushing front. even tho NIST denies the pancake theory.

does NIST have an explanation as to how the majority of core columns were taken out?

does anyone know how MANY were still standing in each instance?

what are your thoughts on the issue? do you think that explosives being used just werent on all of the columns?