Determine the dimensions of the first rectangle.

The top-left corner of the first rectangle is $(5, 9)$.
The top-right corner of the first rectangle is $(12, 9)$.
The width of the rectangle is the difference in x-coordinates:

$$\text{Width} = 12 - 5 = 7$$

The point $(12, 3)$ is given, which is the bottom-right corner of the first rectangle.
The height of the rectangle is the difference in y-coordinates:

$$\text{Height} = 9 - 3 = 6$$

Point A is the bottom-right corner of the first rectangle. From the given information, this point is $(12, 3)$.

$$A = (12, 3)$$

The problem states that the two rectangles are identical. This means the second rectangle also has a width of 7 units and a height of 6 units.
Point A $(12, 3)$ is the top-left corner of the second rectangle.
To find the coordinates of point B, which is the bottom-right corner of the second rectangle:
The x-coordinate of B will be the x-coordinate of A plus the width:

$$x_B = 12 + 7 = 19$$

The y-coordinate of B will be the y-coordinate of A minus the height (since the rectangle extends downwards from A):

$$y_B = 3 - 6 = -3$$

So, the coordinates of point B are $(19, -3)$.

$$B = (19, -3)$$

The coordinates are:
A is $\boxed{(12, 3)}$
B is $\boxed{(19, -3)}$

For the second part of the question:
n stands for a whole number.
n is greater than 30, which means $n > 30$.
n is less than 100, which means $n < 100$.
Combining these conditions, we have $30 < n < 100$.
Since n is a whole number (non-negative integer), the possible values for n are integers strictly between 30 and 100.
The numbers that n stands for are $31, 32, 33, \dots, 99$.