Hey, thanks for the suggestion, but each record already is on a single line in the spreadsheet.
The spreadsheet is actually pretty simple as far as the data ingestion goes. You could think of the spreadsheet as a simple table like this:
card number | Card name | filepath to front template | filepath to back template
as all the fields for the front of the card are correct (and can be kind of thought of as a single column for all practical purposes) and the back of the card is simply one image box pointing at the correct column (and thus file route) in every record when previewed using the Data Merge control panel.
Unfortunately the fronts and backs of the card have to be on seperate pages as this is a requirement of our printing service.
I got the uploader to work so here is a diagram with screenshots showing the problem.