Restore Differential backup file date not displaying correctly in tree

I have a full backup and create differential backups once a week. I deleted some of the older differential backups to free up space on the external drive. After deleting the old backup files I noticed that the newly created differential backup files have the same names as the files I deleted, such as FullBackup5.
Now I need to restore last weeks differential backup. When I open the Restore window, the number of files listed in the tree is correct when compared to the actual number of files that exist in the folder, but the dates listed in the Date tree are not correct. is it possible that the dates for the original FullBackup5 files is being listed rather than the new date for this file name? If so, how do I fix it? How do I detect which date is last weeks backup file?