add the column ReportServer.dbo.Catalog.Hidden to your query.
when a folder or report is marked as "hidden", you have to change the view in SSRS to "Details View" to see those hidden reports.
it's a functionality to hide little used reports to provide a more relevant dashboard kind of activity; semi-archiving little used reports, for example.
each folder or report has a checkbox that says "hide in tile view" if you go to Manage>>Prooperties
Lowell