Having worked in auto assembly plant for 18 years(unfortunately in the 90's-2000's) I know firsthand that engineering blueprints are just "plans" for how it should be done. Everyday the plan needs to change to keep the line moving efficiently and many times a worker is moved to a new job to cover for an area that is short handed that day.
Many times when the worker is moved to a new job he only gets about 10 minutes to learn the job and then is left to figure it out as he goes. Many times when this happens he is just trying to keep up with the line( new car every 49 seconds) so as not to get behind and if the part fits(even if it doesn't) he sends it down the line just trying to survive.
Many other times there can be a part shortage or even a running change to improve flow and parts or processes change accordingly.
As far as a manual for restoring a certain model goes, wouldn't that be nice? But then everyone would be an expert!!!!!