The Pages open panel does not report any quanta of files found in any given folder, so it is useless for your intended purpose. Instead, use the Finder Window to get file counts of each selected folder containing your Pages documents. In the Finder View menu > √ Show Status Bar and √ Show Path Bar.
Now, with a Finder window open, navigate to your respective folder containing the Pages documents, and when you double-click to open that folder, a file count will appear at the bottom of that open window. If you have folders within folders, then Finder will count everything and inflate the file count. If this is the case, you can click in the Finder window's search field and enter the following:
kind:pages
and it will exclude anything not a Pages document in the folder count.
If you are using an Apple Magic Mouse, in System Preferences > Mouse, you want to select Secondary click to enable a right-click to expose secondary menus.