So, word to the wise, check every copy before sending them out the door, whether you think your book has experienced this problem or not! After much practice, I have discovered that simply fanning the pages and keeping an eye on the numerical progression is sufficient for catching this error. This came in especially handy earlier today, when checking the replacement cartons of complimentary copies Harlequin had sent me. Fortunately they had sent me 2 cases, because one entire case contained nothing but flawed copies . . . on the bright side, that's 24 bad copies that won't be finding their way to readers.
For any fans reading this post, I am pleased to report that Harlequin has been most responsive with regard to mailing replacement copies, and their customer service department can be contacted by emailing firstname.lastname@example.org.
May all your books be correctly printed!