When building a data set that will have the output set to one row per form and includes the follow up(s) assigned request status pre-filter, you can set submission status pre-filters in addition to request status pre-filters. This allows you to further limit the data set to only include data from forms meeting the submission status(es) you select.
This is most helpful when you want to run reports to only show assigned/draft, submitted, and/or complete follow up forms.
For example, let's say for your data set (with output set to one row per form) you select the follow up(s) assigned request status pre-filter. You only want to see data from follow ups in the assigned/draft status in your report, so you select the submission status pre-filter of assigned/draft as well. Your report will only include requests with the follow up(s) assigned status. For each of those requests, it will display one row of data for each form with the submission status of assigned (draft).