Thanks for sharing your observation. There is now room in the regular stacks for z books. I checked myself. It's something to think about trying to do. There is shelf space for the Z books.
People get confused.
You are probably correct that there is room right now, however when the materials return that were damaged in the flood this will no longer be true. We are working on better directional signs to help in locating the Z books. Thanks for sharing your observation. Thanks for letting us know this. This is an error on our part.