You are absolutely right. American doesn't fly to BRU from JFK anymore, but it is true that they used to. They had codeshare flights with Sabena until early November when it collapsed.
At one time American flew to three US destinations from BRU: JFK, ORD and DFW all with B767-300ER's. DFW, it didn't last long, JFK, it lasted from 1989 when American started flying to Brussels until 1997, ORD is the only one that remains. Now American is changing it's daily schedule from BRU to ORD although the flight number remains the same, the flight leaves now at 1100AM instead of 230PM, it used to be Sabena's schedule to ORD. The return flight now leaves at 530PM Chicago time and arrives BRU at 830AM. That bothers me a little bit. I used to find it very conveninent for me leaving Brussels on flight 89 early in the afternoon, arriving in Chicaco in the afternoon and connecting on a flight to LGA at 700PM. The return flight, flight 88, used to arrive in BRU at noon. But, that is no longer true, too bad.
What would be great is this: American having a flight from BRU to JFK at the end of the day, exacly what Sabena used to have. The aircraft would be a 767, that I'm certain. Why doesn't American do that? I think they can. They should, really. They took advantage of the slot left empty by Sabena on the flight to Chicago, so they could do the same with New York, taking the time slot in the evening left empty by defunct Sabena. Too good to be true.