Years ago, whilst working for a US outfit. Our company was having a 50-70% failure rate on upgrades. Most of the training dept was ex USAF. During an FAA audit the training dept was red flagged. Heard the inspectors said that if the failure rate was greater than 5% then there is a problem with the training dept. Dim memories of more checking than training happening in those days. Things got gradually better after the FAA keeping a closer eye.
kika