Correct, and no steel can be seen below where it counts. In the construciton photo above, seven floors lower, there was concrete, 60 feet back from the perimeter columns in a dark hole. That construciton photo shows that what you are trying to call core columns has butt plates joining sections together. They are way too weak for a "core column". Only a 100%
fillet weld will suffice.
The videograpers producing the 1990 PBS documentary that has been disappeared, The Engineering and Construction of the Twin Towers", said that good pictures of the concrete core were hard to find for those reasons.
Part of the same video found, certainly filmed at about the same time in construction, but not included in the "Building the World Trade Center", which the 1990 PBS described as inaccurate and misleading, relating to the description of "core columns", showed one exceptional shot at a time when the concrete was actually at the level of the top floor and exposed to daylight. From the background forward was seen: Atlantic ocean, perimeter columns, perhaps 2 interior box columns, form wood of the outside of the concrete wall with large hardstone aggregate, the tops of
rebar, a dark vertical face of concrete.
The only other really good shot was when the sloping top of the pour at a low corner when it happened to have good light on exterior formboards, the corner ripped open, light came almost down the wall line to show perhaps 3 of the huge rebar on 4 foot center. It was a black and white taken by an inspector.