Upvote:15
Turns out the US government keeps records on all the international conferences it attends, and there is no record of it attending any such conference in Lisbon.
Before the war, the last conference in Lisbon attended by the USA was this one in 1934:
43.11.15 Records relating to the third meeting of the International Technical Consulting Committee on Radio Communications (ITCCRC)
History: ITTCCRC established as a result of the International Radiotelegraph Conference held in Washington, 1927 (SEE 43.2.15), and reestablished by the International Radio and Telegraph Conferences held in Madrid, 1932 (SEE 43.2.25), to study and provide opinions on technical radio questions submitted to it by government regulatory bodies and radio operating companies. Third meeting held in Lisbon, September 22-October 10, 1934, to review opinions.
The next one wasn't until the 1950's:
43.7.14 Records relating to meetings of the foreign ministers of France, the United Kingdom, the United States, and the Federal Republic of Germany
History: Foreign ministers of the United States, the United Kingdom, and France met in London, February 17-19, 1952. In addition to meeting among themselves, the three foreign ministers met, February 18-19, 1952, with the foreign minister of the Federal Republic of Germany.
Textual Records: Records relating to discussions of the status of Germany at the foreign ministers' meetings in London, February 13-19, 1952, and Lisbon, February 20-26, 1952. Records of North Atlantic Treaty Council preparations, Lisbon, February 1952.
Its possible there was a conference the USA didn't attend of course, but since the AI specifically said it did, its statement appears to be wrong.