Peter,

Usually if you don’t see all your photos, it’s because some kind of filter is applied. The default view is “unrated or better”, which means if you reject a photo it disappears from view until you manually ask to see them.

In the browser, tap the (x) to reset to the default view, or click on the drop-down and choose Show All to see everything [screenshot].

You can know at a glance how many photos actually live in any one project by enabling the option “Show numbers of versions for projects and albums” in the Preferences [screenshot] which will give you a view like this: [screenshot]

Also remember you can’t import photos into a folder; only into a project. So perhaps you’re simply looking in the wrong place.

If you’re not familiar with that, I highly recommend my ebook “In-Depth Getting Started with Aperture 3” or even the full Aperture training video if you prefer that. There’s also the Live Training you can consider.