I would be grateful if any of you could recommend a good study on the process by which the chapter and verse numbers of texts such as the Upaniṣads and Bhagavad Gītā have been determined.  I recently had a conversation with the editor of a journal for which I had written an article that cited BG 13.4.  The editor thought the verse should have been cited as BG 13.5, but then he found that some editions do list it as 13.4.  This is actually a question that has intrigued me for some time.  How ancient is this system of chapters and verses?  I have always been struck by the similarities between BG 2.19 and Kathopaniṣad 2.19 and wondered if this was deliberate.

Any guidance that can be offered will be most appreciated!  And forgive me if this appears to be an amateurish question.  Being trained primarily in philosophy, my expertise has focused more on the content of these texts than the mechanics of their composition.

All the best,

Jeff