That seems to work.
One way to have it cleaner than people misspelling drop-out points, could be 'dropped out before Dunmail/Wasdale - then you capture everything.
Reasons for not completing: 'ran out of time' splits into 2 bins maybe - 'got lost' or 'slipped behind schedule'. I dunno if having a text box for 'other notes' might lead to elucidation along the lines of 'wasn't fit enough; bit off more than I could chew' or similar, or just be superfluous.