Five pairs I make it, which relate in different ways to items in the same category. My PDM came from 8D and 27D. On 1A, I saw no ambiguity: word for 'titles' plus word for 'on' plus one-letter abbreviation for 'book', all reversed, with incorrect letter in cell 1. If I've missed ambiguity, I'd be pleased to hear about it! The incorrect letters I've got read L to R, once only for checked instance, do make a phrase that describes the items. Let me know if you'd like more....