Understanding the time-complexity of Insertion Sort
As I see this, it is clear that the array is indexed from 1 to length[A] instead of the usual 0 to length[A}-1.

The first statement is executed n times. It is just that (n-1) times it enters the loop and the last time n'th time when j > length[A] it exits from the loop.

Hence it is correctly mentioned that the internal statements get executed n-1 times.