In a 1631 version, there were two glaring mistakes. Deuteronomy 5:24 meant to celebrate god's greatness. Instead it read: "And ye said, Behold, the Lord our God hath shewed us his glory, and his great asse." And in the same edition, in Exodus 20:14, they left out a crucial word with the result: "Thou shalt commit adultery." According to the Geographic, "the printers were heavily fined" for that last mistake.
But my point is---what systems do you have in place to catch your written errors? I think I read Joe Sugarman say he had his sister who had taught English check all his ads. Do you have a regular person that checks whether the piece works overall as well as for errors?
Many professional copy editors say changing the font to a large point Courier makes it easier to catch mistakes. I find printing the copy out points out problems that I didn't see onscreen but I haven't tried the different font.
Some people read the copy backwards and say that helps. And I know reading it out loud helps me. Anything that works well for you ?
Then again, having others check copy doesn't always catch the problem either. I once wrote a story for a local magazine where I misspelled the name of a shopping center named Libbie Place as Libby Place. The editor didn't catch the error nor did two other people he had check it. But one who did was an elderly lady by the name of Libbie. Her dad named the road after her many years ago and that's how the shopping center got its name. I didn't have to but I called and apologized. She was very gracious---said she hadn't meant to make a fuss--- and I did a story about her.