Y01
1aa3 9.0
1bb3 10.0
1cc4 9.0
1dd3 10.0 123 / 13 units = 9.46

Y02
2aa3 12.0
2bb3 5.0
2cc4 10.0
2dd3 11.0 124 / 13 units = 9.54

So my CA would be

9.46 * 13 + 9.54 * 13
--------------------------------- = 9.5
13 + 13

This is obviously an example, but is the process correct? ?

Do dropped classes affect your CA?

Yes it's correct, though you probably could have left it as (123+124)/(13+13) since you don't need to calculate your average from each year before plugging them in. Dropped classes wouldn't affect your CA unless there was a mark given, like if you dropped in the "failure by default" period.