Students can only view grading for the last assignment they submitted. This means if a student submitted a “draft” assignment that was graded, and commented, they will no longer be able view the commenting or grading for that submission once they have re-submitted the assignment.
For the purpose of draft submissions it is best to create two assignments, the draft and final. If you do not want the draft assignment to count against the students select the option to not count the assignment towards the course total. The assignment can still be graded and students can still view the feedback, but it will not affect their course grade.