Were all the aircraft black boxes recovered after the 9/11 attacks?

All four aircraft involved in the 9/11 attacks had black boxes, which include flight data recorders (FDR) and cockpit voice recorders (CVR). The black boxes from American Airlines Flight 11 and United Airlines Flight 175, which were used to attack the World Trade Center, were recovered from the wreckage. However, the recovery of the black boxes from American Airlines Flight 77 and United Airlines Flight 93, which crashed into the Pentagon and in a field in Pennsylvania, respectively, was more challenging. In the case of Flight 77, the flight data recorder was recovered from the Pentagon site, while the cockpit voice recorder was eventually found as well. For Flight 93, the flight data recorder was also recovered, but the cockpit voice recorder was found months later at the crash site in Shanksville, Pennsylvania. Overall, all four black boxes were ultimately recovered, providing critical data for the investigation into the attacks.