Board Thread:Questions and Answers/@comment-24247692-20131203165635/@comment-3361105-20131203171522

I may be totally spit-balling here, but I 'believe #18 is collected in the Batman & Robin Death of the Family trade, along with other Requiem issues. 19-20 are a two-part Clayface story.

Probably not by coincidence, Batman: The Dark Knight's next trade should collect its clayface story, which suggests to me that the two batman issues might be collected in that book.