The listing page always includes the content to be reviewed (i.e. articles that you have neither imported nor ignored). You can choose to also view content that you've imported (the default view), and / or content that you've ignored in addition to the content to be reviewed.
To do so:
From the Import External Blogs page, expand the Screen Options tab in the top right hand corner
Under the Also Include Items section, check and uncheck the options for Already Imported and Marked as Ignored to include either or both in your blog listing page
When you've (un)checked the desired boxes, hit Apply
As a helpful indicator, the description underneath the Import External Blog Posts title will always tell you what combination of articles you're looking at. For instance, the default screen mentioned above, shows:
If you choose to also include marked as ignored items in addition to the to be reviewed and already imported items, you'd see:
If you chose to look at just content be reviewed, and excluded both marked as ignored and already imported items, you'd see:
And lastly, if you wanted to look at just marked as ignored items in addition to the to be reviewed content, you'd see:
Reminder: By default, when you first land on the Import External Blogs page, you're presented with all to be reviewed items, in addition to those that you've already imported to your platform.