We can see evidence of the bottom corner being pushed to the west, over the upper corner and temporarily remaining upright in the following images. The upper corner becomes displaced to the north and east of the lower corner. The upper part of the building fell over the lower north wall, but under a small section of the lower corner, stripping it and leaving it standing temporarily.
The bottom portion remains standing.
The top edge of the standing piece is floor 97 or 98.
This is easy to verify in a few different video clips. Just mark the place on your computer screen where floor 97, 98 is before the building falls and compare it to this standing edge.
A very good view of the NW corner initial failure and early falling: