Siebe said: “I belief, we cannot really say that only what is mentioned in the Canon has buddha’s approval.”
That is NOT correct. The Buddha taught for 45 years, and literally ALL he taught was remembered by Ven. Ananda (and he made sure to get approval of that material from the Buddha) and they were all incorporated to the Tipitaka.
So, it is safe to say that the Pali Canon, Tipitaka, would not have anything significant missing.