When exporting the top 10 SERP report, not all keywords are included. Presumably, this is because Ahrefs doesn't have SERP data for all keywords imported. However, keywords should still be included in the export and a note of n/a could be added to the adjacent rows. As a result of this flaw, I'm going to have to fudge several exports together in order to have a complete single-keyword list that integrates the top 10 SERP data I wanted.