Final Vehicle is concerned with testing and certification and whatever other finishing touches need to be performed. It also operates the repair department, and the 'yard' with all the defect jobs. Our yard was so packed the company was renting new yards away from the factory.

The repairmen who worked in the bays and yard were stone cold experts on the vehicles and they kept written logs. Those logs were typed up and put in the database by the office clerks. These were mostly signal. There were also networked terminals at some stations but not all down the line.

Finding the root cause of an issue was basically like git-bisect. You knew where a part was added and where it ended up. So you just needed to narrow it down. For a high priority issue, I'd go do a visual inspection myself at the mid station before a part got covered by another part. Broken? Go to the mid station between here and start. Not broken, go the other way. We got stumped sometimes, but mostly we could narrow it down pretty fast. For the workers, it's impossible to lose your job so there isn't a care factor about covering up shoddy workmanship.