737 Classic IVSI operation with blocked Capt static vent

[sheppey]

If the captain's static vent is blocked before take off, then both the captains primary altimeter and captain's IVSI should not move after lift off. The first officer's instruments are unaffected. In one 737 Classic simulator it was noticed that the captain's altimeter stays at airport elevation. However, the IVSI instead of showing no movement, (as would be expected with a captain's static vent blocked) in fact showed normal expected rate of climb eg approx. normal 2000FPM rate of climb. A second 737 Classic simulator set up with captain's static vent blocked before take off, showed the captain's primary altimeter and the captains IVSI as not moving after lift off and climb.

Which is correct - given a captain's blocked static vent occurring prior to start of take off roll?

[island_airphoto]

Does the classic 737 have a "classic" IVSI that is a static driven VSI aided by accelerometers for faster response or is it driven from some other source?
That would be the first place to look? One would assume this classic instrument would indicate a climb at first from the inertial response and fall back to zero after a bit with a plugged static line.

[BAM_dk]

A quick look in the FCOM is what it takes.

Vertical Speed Indicators
Two electric or inertial vertical speed
indicators display instantaneous vertical
speed derived from the respective air data
computer or inertial
reference system.