if I rotate an object, do they vertices of its mesh change?

I’ve got an object with a custom mesh, with all the vertices stored. I wish to track these vertices when the object is rotated.
How do i track these vertices or do they even change on rotating.
I want to instantiate another object using the location of the last vertex of this object, after this object is rotated, if I instantiate it using the last vertex I have stored, it gives the location before the rotation is applied.
In the picture, the second rectangle should start from the top-left point of the first rectangle.
Any help is appreciated.

Hi, I found out how to achieve this. I applied the same rotation to the vector3 which referred to the top left corner. This gave me the correct co-ordinates of the rotated top corner.
The method I used to apply the rotation was,

startPoint = Quaternion.Euler(0, -7.5f, 0) * topLeft;

Where 7.5f is the angle i was rotating around the y axis. Thanks.