Manifold Vacuum Advance what am I not getting?

I don't believe he has 200PSI pressure. If he truly did, it would spark knock at idle, with no load at 42 BTDC. I "thought" my slant 6 was at like 195 psi, until I double checked it with a new gauge and then a friend's gauge and it's at around 155. So someties gauges are inaccurate.

Or the timing light is wrong. Or the damper moved. Or who knows?