The book, is an expression FROM truth, attempting to point to truth. It contains SYMBOLS of truth, twice removed from reality.
Because truth expressed the book, the symbols in the book are not necessarily all possible expressions from truth. Truth could conceivably express a million books, all from the same source or mind. They could all appear to take on different forms and use different words, yet essentially say the same thing.
The form of the book, the words used, the sentences, the sections/chapters, is only one collection of symbols, all coming from the same source.
It is entirely possible for that source of truth to continue to express itself in many, many more forms. It is possible that the Course could in fact be 1000 times larger, or a million. There is basically no limit to how many "forms" it could take, provided those forms express or symbolize a consistent source.
This is why it is then important to recognize that, of all the FORMS in the book, all of the words, you are not necessarily getting ALL words that can ever be said about truth, and you're not necessarily hearing every possible clarification.
For example, in the main Course itself Jesus doesn't really explicitly talk about making his body disappear. Yet, in the notes given to Helen later, from the same source/truth, he clarified further by adding extra information. That information is clarifying as to the meaning of various other parts of the Course, especially surrounding resurrection and how we might leave the dream without death being involved.
There are also times when Jesus says one little phrase somewhere in the Course and doesn't really expand upon it, and yet it's a very key phrase which puts many other things into perspective.
There are also times when I really wish Jesus would've gone into much more detail about certain things, especially miracles and some of the aspects of the end of the universe. In other words, if Jesus were present, there would be a lot of questions we could ask Him which would clarify many things. This is why it is VITAL to get in touch with Jesus/Holy Spirit and develop a relationship with them, so that you can learn from them DIRECTLY.
It's important then not to get too hung up on the specific exact WORDS which Jesus expressed, thinking that the FORM of those words is the truth. The form is not the truth, it's just one of MANY possible symbols and expressions. Further additional forms might possibly change your perception of those words and what they really mean.
If for example you will only accept something as correct if it has an explicit quote in the Course that you can point your finger at, then you are getting bogged down in form and are not seeing the metaphysics.
The form of the words of the Course are twice removed from reality. Once removed from reality is the metaphysics, and/or the symbols in the dream. For example, outer space, filled with seemingly nothing but emptiness, is symbolic for the ego's attempt to make God as absent as possible. Bodies are symbols of having an identity God did not create. etc.
When you look at the words and learn from the words, you should learn, or be able to infer/imply, what the metaphysics of the truth is. Stuff like the structure of the dream, the levels, what certain things mean, where they fit, etc... is not always necessarily 100% spelled out in words. You have to look deeper. As you "generalize the teaching", you will gradually build a clearer picture for yourself about how everything fits together.
Some of those clarifications will bring you insight into how, sometimes, Jesus uses words in certain specific contexts which, if taken verbatim, might imply or infer something which is incorrect. Also sometimes He speaks at certain "levels" and confusing those levels produces a lot of confused metaphysics. Some things apply at certain levels and not others.
Also sometimes Jesus uses words which He seemed to have build up quite a specific definition of elsewhere, but uses them quite loosely in "general conversation" in such a way that people then take this and think it's some kind of metaphysical fact. Sometimes Jesus is just simply talking casually and using normal language, how most people would, and not necessarily teaching doctrine in every word.
With enough exposure and learning you should be able to transcend the Course's words and get more in touch with the "core metaphysics" which is kind of hiding somewhat behind the words. The structure of the dream, the proper location of certain levels and their meaning etc, becomes more apparent when you go deeper into it, and Jesus hasn't necessarily "spelled it all out" directly.
We have to be careful not to get hung up on "where does it say that in the course" kind of approaches. Not everything IS said in the course. And yet, some things are true/logically consistent which may never have been expressed.
We also have to beware of thinking that only what is said in the Course is coming from Jesus's authority and therefore no-one else can say anything that Jesus hasn't said. As you transcend the words and get more of the metaphysics you'll be able to extrapolate it and come to conclusions which are completely consistent with Jesus's teachings.
That makes it possible to write additional content, additional words/symbols, based on the same metaphysical foundation, in order to be consistent with Jesus and not contradict his intentions. You don't need to be in his mind of authority to do this, you only need to grasp the basic logical structure of the separation.
There is a lot of material in the Course and it can become quite blinding through its sheer volume and seeming complexity. But we need to learn, in a sense, to forgive it, by learning to overlook its appearance and look deeper to see a closer or more accurate truth. The truth is simple, not complicated, but the ego has a field day with getting caught up in the form of things.