The INS had a different reaction.
"I think it is certainly embarrassing that the letters show up at this late date," said INS spokesman Russ Bergeron. "It does serve to illustrate what we have been saying since 1995 -- that the current system for collecting information and tracking foreign students is antiquated, outdated, inaccurate and untimely."
Bergeron said the INS forms made it clear that actual approval of the visas took place before the September 11 attacks.
Former INS District Director Tom Fischer told CNN that "the letters should never have been sent." Their delivery, he said, was "a case of the right hand not knowing what the left hand was doing."
The M-1 student visa request forms for Atta and al-Shehhi were filed by Huffman Aviation on August 29, 2000.
The forms asked that the men, who had entered the United States on tourist visas, be allowed to change their visa status so they could take a $27,300 professional pilot program that would last from September 1, 2000, until September 1 the next year.
The student visa requests were actually granted months later -- on July 17, 2001, for Atta, and August 9, 2001, for al-Shehhi -- but postmarks indicate the letters of notification were only sent out to Huffman Aviation last week. They were received Monday, the six-month milestone of last year's terror attacks.
The INS said it sent notification to the two men of their visa status change shortly after the requests were approved. Flight schools, Bergeron said, are routinely last to be notified.
The letters to Huffman Aviation were sent from the INS Student Processing Center run by ACS Inc. in London, Kentucky.
On October 25, 2001, the INS awarded ACS a contract to begin helping the federal agency "process the arrival and departure forms of foreign students, businessmen, and tourists visiting the United States," according to an ACS news release from that time.
Leslie Poole, ACS' vice president, said part of the company's job involves helping the INS clear up its backlog. However, she said ACS only processed requests from the INS and played no role in screening any information.
-- CNN Producer Henry Schuster contributed to this report.