The pitot ram air pressure for a given airspeed decreases with higher
altitude. If the static port were blocked (at say, the takeoff altitude),
the airspeed would "indicate" a lower airspeed since the pitot pressure has
dropped for that airspeed as the plane gains altitude. As another poster
commented, the only altitude where the ASI is accurate is at the altitude
where the blockage occurred.


Not really. You should remain at the same pressure altitude. If you
travel to an area with higher or lower pressure, you would be
surprised.