Buddy of mine does commercial sheet metal in Calgary and hit the same wall on a school renovation. The drawings were stamped and everything, but the mechanical engineer used an old structural grid from before they added a fire separation wall. He had 14 prefabbed duct sections sitting on the truck that wouldn't fit anywhere near the layout. Spent a whole day just measuring and relocating hangers because the actual beam spacing was 4 inches off from the prints. The foreman on site kept saying the tape measure was wrong, not the drawing. He ended up eating about 12 hours of labor and told me he'll never bid off those stamped plans again without pulling the actual as-builts first.

Ha, yeah right? Old timers will show you a trick that took them 40 years to learn and act like it's nothing. Meanwhile I'd be out there with a level and a protractor looking like a fool. The funny part is they never write this stuff down either. It's all just locked in their heads until some random apprentice happens to ask the right question.