[aerohead]

I never met Lamar,but I've read about his testing and would mimic his methodology if so inclined.
It was a Road & Track article in a book about Karmann Ghia cars in which a road test comparison of a Ghia, Beetle, and 1600 Squareback offered the lift data.
Is it possible that Lamar tested a Super Beetle,and not the original Beetle?
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As to the longitudinal vortices on the Bug,Hucho says it's the roofline which causes them.
The Beetle's roof contour is what Hucho calls "pseudo-Jaray." It's too fast to be a proper fastback,and the low pressure of separation induces higher pressure from under and besides the car to flow upwards towards the low,attempting to reach pressure equilibrium.
As the streams collide,the shearing forces set up the cyclonic flow exactly as with warm Gulf moisture convecting up into the jet stream.This is what Kamm worked against,lofting the roof to respect boundary layer requirements which also prevented these vortices.
If you compare the Cd 0.495 Beetle to the Cd 0.30 VW 'Student' concept,you can see how VW has corrected the roofline to kill any chance of vorticity.