I believe this to be one of the long propagated myths. Pressure plates are manufactured and balanced separately. Clutch plate is not balanced at all. There is no way that during the initial build somebody took pressure plates and clutch plate (and flywheel), spun them, moved them around to find the best fit. Even more unlikely is that they balanced them as a unit.
I wonder if the marks that are found on the some plates are nothing more than "I torqued the bolts" check from the factory.
But I have been wrong once or twice before.
Either way I have assembled a couple "randomly" with no issues.