He is what I know to be fact, keeping in mind I have been involved with dealership service continuously since the mid-80s. When the customer bring a vehicle in, the concern is documented and verified. The technician then follows the outlined diagnostic procedure to determine the origin of the failure and the needed repairs. They then go through what ever authorization process is required by the manufacture (sometimes even requiring an inspection by a rep, although rare), they then order the parts from the parts department through the normal PDC (parts depot). On ocassion, something the size of an engine may be drop shipped from plant or supplier. The repairs are then made and the old parts are retained for a time period for inspection if requested and then scrapped once authorized. The vehicle is then returned to the customer and the claim processed for payment. The dealership is then required to retain the paperwork for a designated time period, the manufacture does keep records but I don't know for how long and of course after 40 years it is doubtful it still exist other than what a customer has or some extreme pack rat dealers. This process and core steps have been in place since my first dealership and although I was not involved I am reasonably sure the process was similar in its core since the 40s or 50s but surely by the 60s.
During this this process there are many opportunities for individuals to stray from process. Not diagnois it properly (don't get me started), parts not returned and retained, parts not properly scrapped, the wrong engine given out and the paperwrok corrected to show the right part number for submission purposes (have a $4000 claim held because a parts man gave out the wrong engine and see what happens). I have known of cases where old stock is converted to good numbers to get it out of inventory, sometimes legit with part numbers superseding to a new number, sometimes not. Part of my business is creating these processes and helping dealerships avoid these errors.
Hope it answers some questions.