I'm all sorted now thanks.
I exported all the Aspects I was after with a Grade_Value and Grade_Set_History_ID
I exported all the Grade Sets with Grade, Value, and Grade_History_ID
Then INNER JOINED the two with external code to map back to the initial Grades entered by teachers on the system.
(for anyone else reading this in the future, you will also need to export and map in both reports the Grade_Order if you are doing Fine Grade reporting - i.e a B1, B2, B3 each carrying the same grade value...)