О происхождении махаяны

Зависит от информации, которая добавляется/убирается, но не суть. Виная сарвастивады строже тхеравадинской на 26 заповедей, внимание вопрос, почему тхеры похерили винаю? )) Ну или вот пример попроще, в П.К. входит такой знаменитый текст, как Dhammapada и этот палийский текст является самым коротким их всех известных текстов дхармапады на санскрите и пракритах, внимание вопрос, почему тхеры похерили дхаммападу? ))
Вообще примеров можно накидать много, но тема не об этом.

Сутты Никай содержанием своих текстов, так чтоб полностью, то не совпадают с Агамами.

About 450 years after the Buddha a famine struck Ceylon. For twelve years food was so scarce that the Order of monks was almost decimated partly, we are told, due to some of the laity turning to cannibalism. Some of the Suttas were in danger of being lost. Monks who were too weak to stand rehearsed the texts where they lay. When at last the famine ended, it was realized that the texts needed to be put into writing for their greater protection.[47] Not only the famine but -- according to Adikeram (op. cit., p. 79) -- the danger of frequent invasions from South India, the entry into the Order of irresponsible and irreligious people (on which point see Mahavamsa 33,101), and the fickle favour of kings also played a part in this decision. Accordingly, a Fourth Council was convened, wherein this was accomplished.

It was seen how, during the famine that broke out in the time of King Vattagaamani Abhaya, a great strain was put on the continuance of this form of preserving the teachings of the Tipitaka. When conditions became normal, the members of the Order considered that they could lose the teachings if any similar calamity or calamities were to occur in the future, and they decided that the time had arrived for committing these teachings to writing so that they might be preserved for future generations. The advent of schisms about this time might also have weighed strongly in favor of this decision.

Thus the members of the Order assembled at the Mahaavihaara at Anuraadhapura, took counsel together, and with the permission and encouragement of the king a convocation was held. The teachings were recited and scribes were engaged to commit to writing, on palm leaves, the Pali canonical texts (the Tipitaka) consisting of Vinaya, Sutta and Abhidhamma, and the Sinhalese commentaries. According to the Nikaaya Sangraha, a Sinhalese work of the fourteenth century dealing with the history of the Buddhist order, after the convocation at the Mahaavihaara at Anuraadhapura, the selected number of reciters and scribes, 500 in all, went to Alulena (Aluvihaara) cave temple close to Matale, in the central province. There in retirement they completed the work assigned to them and thus for the first time brought out in book form the teachings of the Buddha.

In the centuries after this Council the texts continued to be preserved as much by recital as by manuscript, for making even one handwritten copy of the five Nikayas, of the Vinaya, and of all the material that had evolved and survived alongside them, the Abhidhamma, the Commentaries, the Chronicles, and so forth, would have been a labour of many years and then the manuscript had to be preserved against the manifold dangers of destruction. But by this time the Suttas were firmly embedded in the minds of those who learned them as being sacred and unalterable by as much as a single syllable.

А что здесь за entry into the Order of irresponsible and irreligious people?

Еще одна возможная причина - это то, что благосклонность, короля в то время, вроде как, была направлена, скорее, в сторону новосформировавшейся школы Абхаягири. Так, запись происходила в удаленной от столицы вихаре, при содействии местного вождя, а не короля, как можно было бы ожидать.