Possible Clues:

• Galley goof
• Maturer sort of mistake
• Mature display concealed ring-leader's mistake
• Mistake in printing
• Unsure comments about quisling a mistake
• Funeral attendant to embrace a bishop when rising is a mistake
• Typographical mistake
• Printing mistake is dumb, keeping a bishop up
• Slip put right near the back of a book
• Sweetheart's suspicious catching betrayer's mistake