When speaking about a textbook used in class, it's a fairly common occurrence that teachers are unable to complete the book by the end of the scholastic year (or semester) especially if they have used supplementary material or the same textbook has to be studied the following year.
To dip into a book suggests that the book itself might not be very interesting or useful, if it were we would spend a greater time reading or studying from it. That expression is more commonly used in conjunction with epic novels or hefty volumes, think of an encyclopedia. How many people actually read an entire book set from beginning to end?
Furthermore, a dip, if you consider one of its meanings is a quick "dive" into liquid to then reemerge. Ergo we dip biscuits into teas, we dip our toes in the water to test its temperature, and we dip our food into sauces or creamy mixtures.
The addendum says that the class covered only several chapters, the expression used by the OP is perfectly suitable, and one that is universally recognized. In fact Google books records 76 results for "we covered chapters".
I would suggest that a sentence similar to the one below, explains the situation adequately.
In this course we covered chapters 5-10, and plan to complete the book by next semester/term/year.
If we substitute the verb covered with dip, the meaning changes quite dramatically.
In this course we dipped into [textbook name], and plan to complete it by next semester/term/year.
The above sentence seems to imply that the class studied extracts in a haphazard, casual and superficial way. The Free Dictionary defines dip as: To read here and there at random; browse Contrast it with the verb, cover, which means all of the following: to deal with; treat; examine; investigate; refer to and you'll see why I have my reservations. Likewise the same is true for: browse; skim; scan; flick though, and leaf through all of which suggest a smattering of knowledge, where nothing is read nor understood in any detail.
Finally, the OP's request for a single word which expresses the concept of studying a few chapters in a book to return to it sometime in the future is unrealistic. Such a complex concept needs explanation. But we do have the phrasal verb put aside (also set aside) which means turn away from and put aside, perhaps temporarily, and place to one side.
A literal fit would be hindsight bias (wikipedia).
Hindsight bias, also known as the knew-it-all-along effect or creeping determinism, is the inclination, after an event has occurred, to see the event as having been predictable, despite there having been little or no objective basis for predicting it.
It's also sometimes phrased as "Hindsight is 20/20," referring to the standard measurement of "perfect" human vision. It's a noun, so it fits your second example smoothly.
Jane experienced a feeling of hindsight bias when she finally completed the puzzle. Of course it was so blatantly obvious she realized she knew how to solve it all along.
I admit this answer is a bit cheeky, because you're looking for something that means they literally knew it all along, whereas hindsight bias is actually saying they didn't know it, only think they should have known it after the fact. As a counterpoint, I offer this: if Jane really knew the solution to the puzzle, why didn't she get it immediately? Or, if you really know this word exists, why did you have to ask the question?
My real point is that human memory is fallible. Just because you think a thing doesn't make it so. It's a fascinating article; I suggest reading the whole thing before you decide any understanding is inevitable. Consider this snippet:
Research shows that people still exhibit the bias even when they are informed about it. Researchers attempts to decrease the bias in participants has failed, leading one to think that hindsight bias has an automatic source in cognitive reconstruction. This supports the Causal Model Theory and the use of sense-making to understand event outcomes. The only observable way to decrease hindsight bias in testing is to have the participant think about how alternative hypotheses could be correct. This makes the participant doubt correct hypothesis and report that they would not have chosen it. However, this only decreases the hindsight bias, and there is not a solution to eliminate it.
For a real word that fits your expectations (or at least, what I think your expectations are), consider inevitable/inevitability:
adjective
1. unable to be avoided, evaded, or escaped; certain; necessary:
an inevitable conclusion.
2. sure to occur, happen, or come; unalterable:
noun
3. that which is unavoidable.
Source: inevitable. (n.d.). Dictionary.com Unabridged. Retrieved July 13, 2015, from Dictionary.com website: http://dictionary.reference.com/browse/inevitable
Jane experienced a feeling of inevitability when she finally completed the puzzle. Of course it was so blatantly obvious she realized she knew how to solve it all along.
Best Answer
Dormant
Other possibilities are latent or quiescent.