i think you're on to something. the imported steel level agreements (limited cheap foreign steel perhaps not made to US specs) started 1968 and continued through 1972, until market demand and high prices made them unenforceable (essentially).
according to Wiki for twin towers construction, the steel was ordered in small batches vs large quantities from Bethlehem steel or US steel company. Interestingly, Karl Koch was the company tasked with obtaining some of the steel.
Wiki
Twin Towers
Construction work began on the North Tower in August 1968 with construction beginning on the South Tower by January 1969.[137] In January 1967, $74 million in contracts were awarded to the Pacific Car and Foundry Company, Laclede Steel Company, Granite City Steel Company, and Karl Koch Erecting Company to supply steel for the project.[138] The Port Authority chose to use many different steel suppliers, bidding on smaller portions of steel, rather than buy larger amounts from a single source such as Bethlehem Steel or U.S. Steel as a cost-saving measure.[139] Karl Koch was also hired to do all the work of erecting the steel, and a contract for work on the aluminum facade was awarded to the Aluminum Company of America.[138] Tishman Realty & Construction was hired in February 1967 to oversee construction of the project.[140]