What are some notable scams in history that went unnoticed for so long?

Surprising that no one noticed the double prime symbol for inches instead of the single prime symbol for feet. The scammer was like "well, I didn't lie, you weren't careful enough and it's not my problem!".

Wouldn't they have noticed that there were only 3 stories of windows on the blueprint?

Wow. I hadn't heard of this. What a clever (and shifty) scam.