Historically they think it was about 300 years after he died that it finally got written down. At that time, they believe that they were written correctly by other fully enlightened people, so as to when they were written, they were considered to be correct, a true record of his teaching. Two thousand, two hundred years later though, what we have today, does not appear to be absolutely correct, there are many people who have studied the scriptures quite a lot, who consider that there are some areas where something is wrong. An example, I read about once, is when the Buddha mentions that he will teach six things, and then only five things are taught. So the scholars who have studied this believe that there is a paragraph missing, it has been lost or the five became a six, etc. There are other people who study the style of writing, and they are able to basically judge what time in history the style was used. And there are some scriptures that have a mix of style, which they feel would not have been correctly done. So there are little points that scholars and historians feel are imperfections, shall we say, in the scriptures. However, according to my own personal understanding from reading the scriptures, most of it is very good, and worth a lot.