All 3 rows have to be filled out. Each row represents 1 final composite. SPA wil pull all of the data for that row to use for that composite. It will never use data from a different row.
The reason is because each PSD template may have different needs. For example, in one template the LASTNAME text may use resize mode X and the other template may use XM. So it need to be able to get the correct value for each. Another exmaple is the text field for each template may be different. In on PSD, you may be using NAME for the full name in one layer. In another PSD you may be using FIRSTNAME and LASTNAME in 2 different layers. So in that case you would have columns for FIRSTNAME, LASTNAME, and NAME. The in each row, you would have the correct data to go along with the Template File in that particular row.