Comment by buildsjets

The article does not mention it (that I noticed), but the lower floors were occupied and in use before the upper floors were completed. My father was a beat cop in Manhattan in the late 60s and early 70s, he tells me that the construction crew took him up the elevator to a floor where the windows had not yet been installed, while businesses were working in the lower floors.

Dad also bemoaned the loss of Radio Row to build the WTC, as he was a big Ham enthusiast as a kid.