@Jim.Z.938 There is a sample grade import CSV file you can download, linked under Assessments → Grades → Enter Grades tab and the blue Import button.
OK, got and did all that. Downloaded/Saw sample file. Interesting columns especially the first one called "OrgDefinedId" which comes from where? So it looks like you do have to—after getting the columns you want into BS—you have to upload the gradeless grade page, otherwise, again, what/where are these "OrgDefinedId"'s coming from?