I retook Higher Drama (cos I failed it miserably) last year, and Higher Business (because I got a C and knew I could do better).
In Drama, I didn't need to resit the NAB's. On the contrary, I was allowed to sit the AH NAB's so I could at least get a partial AH Award.
However, in Business, I had to resit all the NAB's, which was a real pain in the butt. But hey, I already knew the course, so it wasn't too difficult.
Sometimes resitting the subjects was a bit of a drag cos it was really repetitive. However, when you seen an improvement in your grades from the previous year, it was a real boost.