There is only one row for an image series in the spreadsheet exports, and no data that indicates that it is a series. Seems like there should be information on how many images are in the series, the ID numbers and file names for each. Is this in a different export?
Each row represents a submission, whether it’s a single image or an image series. The first column contains the submission ID.
When using the bulk image download, the file names are generated with the following information:
The first block in the file name is always the submission ID, so you can easily see which image(s) belong to which submission.
I will add an image count as a feature request and let you know once we have an update.