My approach... Create a form as you normally might with a hidden field called "prestage" and "poststage" and the relevant rating fields. Make the default value [get param=prestatus] for the prestage hidden field and also [get param=poststatus] the poststage hidden field. These are parameters we are going to dynamically fill in and it will help us understand what entries are associated with which stage of the workflow. These will hold pre or post stage status. Maybe that will be "course1-presurvey" and then another would be "course1-postsurvey".

On the page where they fill out the form the first time, insert the form shortcode and set the parameter within that shortcode.

Example: [formidable id=x prestatus="course1-presurvey"]

On the page where they fill out the form the final time, insert the form shortcode and set the parameter within that shortcode.

Example: [formidable id=x poststatus="course1-postsurvey"]

When complete use a view to create the output you want using math shortcode: https://formidableforms.com/knowledgebase/math-calculations/#kb-operators (You can use field IDs to grab dynamic values from the field values instead of static values).

Caveats: A single form cannot be active on the same page at the same time. Also a user could theoretically fill out the form more times than intended. You might then refer to the date and times of the submission.