Aperture flummoxed me for a bit this morning. I have a project with a few hundred images in it. The project also contains several albums, just the regular kind that I have dragged some images into. When I would click on the project, though, I saw only a small selection of images.
I clicked on another project and every image in that project was visible, even ones that were included in albums within that project. When I clicked back on my first project, though, I saw only a smattering of images.
It turns out that the Query field - the one directly above the right side of the browser pane - is specific to every project in your Library. In other words, once you set the query field to something while viewing a project, it stays that way until you change it.
So, my first project had a query set, but my second project didn’t. If you find an odd assortment of images displaying in a project, remember that you may have performed a query at some point, and not reset it when you were finished.