The drawings, being made after the fact to fulfill a contractual requirement, would leave crucial details out, and were never checked for accuracy.
If you farmed the drawings out to machinists to make the parts, they would not fit together.
One of the things I did in my engineering work at Boeing was to work out the tolerances for each part. The idea was that if the parts were within tolerance, they'd all fit together. If the tolerances are missing or incorrect, then you're in for a lot of very expensive rework.
Some of the engineers were incompetent, and when the first run of parts were received, they could not be fit together. I'd be assigned to fix it. The assemblies I worked on all fit together first try.
The stab trim system had very powerful motors, and if the jackscrew nut was run into the stops too many times, it would tear it apart. So there was a mechanical cutoff system with cables and levers which would turn the motors off between 1/4 and 3/4 turn from the stops. It was not adjustable, since Boeing did not trust mechanics to adjust it properly. So, it relied on accurately machining the parts. I got the job of figuring out all the tolerances.
On the first build, I got a call from the factory saying, since I'd designed it, I get to be there for the first rigging. I arrived, and the seasoned mechanics laughed at me (I was very young) and said the rigging never worked the first time, and would have to be redesigned. We all crawled into the fuselage behind the rear pressure bulkhead. They manually set the cables to have it 1/2 turn from the bottom stop. Then they chortled, said they were going to break it, and turned the motors on. (Those motors make quite a racket.) They watched the stab trim go full travel to the top. The cutoff system shut off at exactly 1/2 turn from the end, dead center in the tolerance zone. I said "bye guys", climbed out, and went back to my desk.