Possible Clues:

• Keying errors dame made from form, for example
• Proofreading finds
• 17-Across targets
• Errors like "yhis"
• Editors remove them
• Copy editor’s catches
• Errors when texting certain blood donors, we hear
• Mistakes in the starred answers? (read the "wrong" letters in order for a bonus!)
• Resume no-nos
• Printed slips