I approved an ad that was written incorrectly. My instruction to the agency was to write ". . . as little as 3 classes" but the agency wrote "as little as 3 credits." I did not catch the mistake before I approved it. No one have noticed the mistake so far, I just discovered it today when I was filing old project folders. The ad was an newspaper ad and it went out over 2 months ago. The mistake will not affect furture projects. I feel really bad over it. I can't believe I missed the typo. There is a chance people will discover the mistake later because we save all final artworks on the share drive and keep a hard copy of the ads in a binder. We also reference old ads from time to time for copy ideas. Should I just say something to my boss about it or just let it slide?