All very interesting.
Some of the "gotchas" on these gyro tests is that they can be slightly imbalanced to induce a drift of any rate desired.
The only way to know if you have them really balanced is to see if they have drift, then invert them and operate them upside down, or spin the weight the other way, and see if they drift the same way or the other way.
In other words, you could "balance" them out so they had no drift, even if the earth was rotating by setting an artificial drift rate that compensated.
In fact I had an old timer aircraft gyroscope repair guy tell me a decade ago how he'd ask the small plane customer what their latitude was and when they sent him gyro compasses to calibrate, he'd adjust the little weights inside to get a drift that would counter the earth's rotate at that latitude to minimize the drift for the area the small plane usually flew.
So when I see a video of a gyro humming away with no drift, all balanced out with tape and putty and whatever, it's really cool, but we have no way of knowing if it was balanced in such a way to eliminate the drift at whatever latitude it is, in which case possible earth rotation would have been masked.
Ideally, the gyro would be balanced out with no drift while the axle was pointing at the north star, and the test would be done at near 45 degrees N or S latitude.
Then the thing could be rotated 180 degrees on a level surface without adjusting anything else, and then the axle would be 90 degrees off from the north star, and if the earth was rotating, then suddenly a drift would be seen.
I was playing around with an old vacuum driven gyrocompass I have but could not get it very stable because the air jet on the weight creates various forces which cause drift which depends on exact RPM and air pressure.
I may have to use an electric one -- or maybe just a large free spinning wheel in a vacuum -- spin it up with compressed air then cap the jar and draw a vacuum to reduce air friction.