peace ichephren,
I'm surprised by these types of questions. The reason for my surprise is because the answers are within us and are easily observable, even today.
Do you not recall what happened to Jesus and Moses for example? Is what they did/said here with us today perfectly intact? Or has it been added, subtracted, embellished etc? Do you not know of any local urban legends/myths in your area? Have you never been in a situation where an event happens and you recall it differently to others?
What if the primary medium for communication was oral (like it was back then) how easily do you think it would be to create stories? It would be much easier! In fact that is the very reason the so-called science/isnad of traditional hadith came about, if there was no distortion there would be no need for checking each report.
The information we need about the messengers are in 'the reading'. Why is it important to know about what The God deemed unworthy to mention and thus left it out? Who knows better? The very first descriptive word used to describe 'al quran' (apart from a writ/kitab) is 'hudan', a guidance, a direction. That is its purpose, plain and simple.
How does one verify a guidance? If you buy a desk with assembly iinstructions, how does one verify the guidance received with the desk is correct/truthful? This is truly the key to understanding this life.
To those who question (like I do), an internal verification system is contained within 'the reading', therefore it becomes irrelevant to know who colelcted it or put it together. It stands on its own, and it can only be defeated on its own. Like most books, like most truths, it is its contents that determine its integrity. The truth can withstand scrutiny of any kind, and in fact, we are encouraged to scrutinise it. That is how its verified.
If you have not already done so, please read a brief account of the history of hadith & sunna within Islam here:
Summary of 'Rethinking Tradition in Modern Islamic Thought'Wakas
