Hi Maureen,
Great question. Jason actually covers this question in our Bulk import video (link goes to the time-stamped section).
In short, the Photo Review page is a temporary storage space of imported photos. This is the first step of the bulk import process. The second step happens when the spreadsheet is uploaded and connects the data to the images from that temporary folder.
If any of the images get re-imported with the same file name, the new image data will overwrite the image in that temporary folder, but historical data that has already completed the second step of the bulk import process is left alone.
This is doubly confusing when we’re talking about deleted imports, because it makes it seem as though the old data is still in the system, when it actually isn’t.
This is by design, but I also think this is an example of something that makes sense from the engineering side but not from the user experience side. I’m going to change this to a feature request because I’m sure others may agree that seeing these ghost filenames is confusing.