Z: Were they drifting ? Hard to do with a rate gyro.
Actually, its easy to advance the urban legend about yawrates being different front, rear, left right, top and bottom because of many reason:
Cheap gyros (they're relatively low cost anyways) are commonly solid state comprized of hundreds or even thousands of little bits that all vote for concensus on what the actual median turning rate is. As they wear out, blue states turn to red states. Having a set from different batches will indicate a severly bent up car. Of course, no-one would be so thoughtful to mount all two or three in the same spot and realize that there could be differences in a calibration test. Nah, that would require a note from a stockholder's meeting.
You can buy rate tables to calibrate your instrument(s). Even a WW-II bomber gyro will still do a good job but it requires 24V - 28V and will affect your effective weight distribution.
Some still subsrcibe to the multiple lateral accelerometers (front, rear and center) to use in their cleverly perceived method of integrating sum and difference signals to get yawrates and angles, etc. The thing worth noting is that you'll even have a hard time doing this with perfect simulation outputs, much less with the stuff from your rolling trash compactor.
My most memorable gluten free wiggly frame with several rigid body yawrates had bad breath and required a faceless filter to get a good signal to noise ratio. (Its called a pillowcase filter in Matlab).
Still waiting for the money shot....