Understanding the possible reason for the clutch failure

Andrew from ASR picked up on an issue today that was missed in the previous install and most likely would have been the cause of the clutch failure.
Using a flat ruler he checked the flatness of the clutch discs and found them to be bent out in the center, this was very odd and along with the failure of the retaining plates, which he had never seen before just didn't seem right.

In the installation instructions it shows that 4mm must be taken off the center shaft otherwise it can cause a failure.

Checking with another box he was able to confirm that that 4mm was not taken off the input shaft which meant the center bearing was pushing too far into the center of the clutch and bowing out the clutch discs eventually causing the retaining plates failure.