According the publisher's details given for volume four, we know that at least up to chapter 43 ("The Steed Balaha") has been published. As I personally only have the first two volumes, I can't tell you if any of the subsequent chapters are included in volume four, or if they are to be published still. There are supposed to be 54 chapters in total, based on the table of contents given by Karma Chagme (as published in the first volume).
It's sort of unclear if the fifth volume is supposed to be the root text or not based on the description given on the KTD bookstore website. However, keep in mind that "[Khenpo Karthar] Rinpoche also omitted the chapters that he considered restricted. These restricted or secret parts will be taught and published separately at Karma Ling Retreat Center for use by qualified students."
It's possible to get the root text in the Tibetan if you can read it: http://www.namsebangdzo.com/Karma_Chakme_s_Mountain_Dharma_p/13488.htm
"The Sutras, Tantras, and Philosophical Scriptures are great in number. However life is short, and intelligence is limited, so it's hard to cover them completely. You may know a lot, but if you don't put it into practice, it's like dying of thirst on the shore of a great lake. Likewise, it happens that a common corpse is found in the bed of a great scholar." ~ Karma Chagme དྲིན་ཆེན་རྗེ་བཙུན་བླ་མ་རཱ་ག་ཨ་སྱ་མཁྱེན་ནོ།