NY Times for 17 May has a front-page article on changes in NY City building codes. In the continuation on page B4 there's a sidebar "History Rewrites the Rules" listing the years of various changes, and the last is 1968:
"1968-- The building code is rewritten again, allowing for new, lighter-weight materials and spray-on fireproofing. Previously illegal techniques, like those employed in 1962 to build the T.W.A. terminal at what is now Kennedy International Airport would now be possible in New York City."
The article says nothing more about it. What, if anything, was illegal about the Saarinen terminal?