There were 2 other nest boxes at KP. One was on Building 59 which was demolished, so it got taken down and presumably destroyed.
The nest box is gone, but B-59 is still standing.
There is speculation that the B-83 and B-59 nest boxes were taken down as part of the preparation for the demolition of several nearby buildings in 2006-7. If falcons had moved into either of the nest boxes, they would have been inside the blast zone.
As for the two nest boxes, someone should walk up to the top of the stairwells of B-59 and B-83. I wouldn't be surprised if the nest boxes were still there tucked into a corner.