剛幫你查了一下, AA 值大多都是單指(ex. Sandisk)

Reserved Block Count : This attribute is used to count the number of reserved blocks used to replace bad blocks.

不過確實有看到(ex. Kingston)是把兩個併在一起的(Early and Later), 你參考一下

Counts the number of Bad blocks.
Raw Value Byte [1~0]: Early bad block count
Raw Value Byte [5~4]: Later bad block count
Formula
MABN: maximum acceptable bad block number
CBBN : Current bad block number
Spare unit percentage = ((MABN - CBBN)/( MABN)) *100
This formula calculates percentage of spare blocks. Value will range from 100
to 1.