time machine- some backup dates not visible

I have been backing up using Time Machine using the Back Up Now feature since I bought my Mac Pro, but have never needed to restore anything until today. Because I accidentally overwrote a file with older data, I wanted to restore from the backup that I made yesterday in Time Machine. I discovered that the last dozen or so backups are "black", that is, the Finder window for the backup date is shows as black. When I click on the arrow that moves to past dates, it passes all of the black Finder windows and stops on the first viewable finder window, which happens to be dated all the way back to 2011. I cannot seem to access any of the "black" finder windows with more recent dates.

What is going on, here? Is there some kind of glitch that is not enabling me to restore from these black Finder window screens? That would be awful.

I hope I can get some help with this. Thanks---