I thought it was accumulative?
My first year of college I was going to do 5 but then for a couple of reasons I wound up only doing 3, second year I didn't get the grade I needed to continue with one of them so I finished the other 2 A Levels and picked up a third AS course, and this year (3rd year) I'm finishing the new course and have picked up 2 AS to pad my timetable.
When I went to put it on UCAS I could put the completed A Levels as completed with definite marks and the ongoing one as pending, so long as I put the date of the qualification received down, and unis see it as 3 A Levels and 2 AS Levels, even though some of them were started 2 years apart.