If you have seen the
MayDay series (if not, I really recommend it) there was one chapter about the
Aeroperú 603 crash. Let me quote from the wiki
As a result of the blocked static ports, the basic flight instruments relayed false airspeed, altitude and vertical speed data. Because the failure was not in any of the instruments but rather in a common supporting system, thereby defeating redundancy, the altimeter also relayed the false altitude information to the Air Traffic Controller, who was attempting to provide the pilots with basic flight data.
This stuck to me as the most vivid reminder that ATC can not obtain the altitude independently of the airplane's instruments (other than, as previously stated, an aproximation by the military)