Bias-ply tires overgripped?

I'm messing around with manual performance testing again and a completely stock Autobello Piccolina 110 A is putting up pretty consistent 0.78g readings on Grid Small Pure. This is roughly in line with a radial-shod early-1990s sport sedan and is actually about what I got from an ETK 3000i in similar testing a couple years ago.

In 2019, Motor Trend tried to do an instrumented test of the Kurtis Sports Car that was on their first 1949 cover, presumably using modern reproduction bias-plies. Apparently, the tail started to drift slightly at 0.50g, so that's the figure they used for the test record.

 

i suppose because the pickle is lightweight. i could be wrong though. the etk's are heavy cars, no?

 

Moonhawk 378 (F78-15 bias ply): jumps around between 0.75-0.78g until it scrubs off too much speed. Can have transients over 0.80g depending on how you prod it.
Burnside Special (800-15 bias ply): peaks at 0.64g, seems able to maintain 0.62 with a lot of steering angle. Still better than the much lighter Kurtis did IRL, somehow
Gavril Barstow 423 non-RS (695-14 bias ply): 0.72-0.73g, albeit with the back end slowly slipping out the whole time
Gavril Barstow 353 RS (E70-14 bias ply): 0.76g
Gavril Bluebuck RS (735-14 bias ply): 0.72-0.73g, but you have to throw it in just right or the rear tires will be slightly underused
Ibishu Miramar (560-13 bias ply, same tires as Autobello): 0.65g, throwing it in does not work

Obviously Beam's BPs are pretty sensitive to suspension type & settings along with how you drive them, and there may be a difference between the older 560/695/735/800 type and the newer E/F type bias plies, but even the 4000lb parade float from 1953 has way more grip than it seemingly should, even if MT may have been reluctant to fully wring out the Kurtis

 

seems i was wrong