Little Notebooks

In the movies, little palm-sized notebooks are carried around by journalists, detectives and the victims of head trauma. They pull them out of pockets and purses and take random notes or refer back to them for information they're just sure they wrote down. Sometimes all it takes to throw the hero off balance is to take a page from the notebook. These little notebooks are amazing things. Always with plenty of paper left for notes and yet they're simultaneously filled with all sorts of useful information already.
The thing is, I've seen these little notebooks in the store while shopping for real notebooks. You know the ones, their cardboard covers in primary colors, white paper with blue lines, spiral-bound along the top. Or maybe, if the user is a veteran detective or journalist then the notebook is the slightly more respectable flip-top refillable style or the Moleskine "Journalist" edition. No matter the cover though the little notebooks are never new. They always appear to have been loved worn abused for years. But when seen on the shelf they only come with somewhere around fifty pages.
Bearing all this information in mind, I've always wondered about their usefulness. I have to imagine a journalist takes a lot of notes and although I have heard stories concerning good reporters and systems of coded short-hand lest some aspiring Wolf Blitzer wannabe snags their notes and scoops them on the story of the minute. Even still, if they take notes (and by "they" I mean journalists as characters not as people. I don't know any journalists as people.) as copiously as depicted then the effective usefulness of a notebook is two, maybe three, stories.
As for police work, I think the distribution would be a little different. Were I a movie detective, or better yet a television detective as they handle a lot more cases, I think I would want notes for each case in its own notebook. That way I could toss the notebook(s) into the case file when everything was all wrapped up. Realistically though, this would mean that a detective in a respectably-sized city would probably at any given time have somewhere between two and six notebooks to keep track of, with at least a couple freshies ready to go for new case assignments.
But the biggest mystery is the note-taking of the walking wounded. In the movies your average head case stops to take notes at least four times a day. That's an average trauma, not a far-fetched and unrealistic injury like the guy in "Memento". Four times a day, fifty sheets per book. And they never use the back side of the paper. Plus everything is printed in large letters with plenty of space between notations, either because they have reverted back to fourth grade handwriting or for our benefit as observers. Four times a day, fifty sheets per book, and we'll figure an average of two notations per page. So lets think of a character as an actual person with a whole life to live, not just the few days weeks months of a movie, which means maybe they go through one a month. And they're constantly flipping through them, checking for a bit of wisdom that they wrote down god knows when. (We won't even address the fact that the information they need is always accessible and in order, despite having gathered it at different times.)
So my question is this: What happens when the little notebook is full? Do they toss it onto a shelf in the closet and grab a new one and start over? Do they write dates on them so that maybe they can piece their year decade life together some rainy Tuesday evening? Do they take the time to copy truly useful information into the new book before storing the old one? Or do they just chuck it out and start anew?
Without some sort of organization and retrieval system information loses its value. If you can't recall it, you don't have it. Regular people would know to get on the number six bus to downtown to go to work, but the trauma victim would have to write that down and if it's not in the notebook where they expect to find it then they effectively don't know it. So when a new notebook becomes necessary, are the first few pages dedicated to necessary knowledge like the number six bus and their mother's new husband's name? What if they forgot to write that down in the new book? What sort of havoc would that wreak onto their lives?
I am constantly confused by little notebooks.