In order to show all items in your Pages library in the "Navigation Editing and Sorting" navigation pane, you would need to make a slight change to your web.config file on each Web Front-End server in your farm.
Step 1: Open your web.config file and search for "CurrentNavSiteMapProvider"
Step 2: Add the DynamicChildLimit=”0” property to this tag as in the code snippet below
<add name="CurrentNavSiteMapProvider" description="CMS provider for Current navigation" type="Microsoft.SharePoint.Publishing.Navigation.PortalSiteMapProvider, Microsoft.SharePoint.Publishing, Version=14.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" NavigationType="Current" EncodeOutput="true" DynamicChildLimit="0" />
Once you have saved your web.config file you should see all your pages in the "Navigation Editing and Sorting" navigation pane.