How to know Lord Buddha Said "That"

Since anyone in this world can come up with theories/definitions which can claim to be Buddhism, I follow these rules generally to validate if in doubt.

1. Must fit to the theory of Patichchasamuppada
2. Must fit to Raaga vinaya, Dwesha Vinaya, Moha Vinaya
3. Must fit to Four Nobel truths.

BUT, since we still have a written book called Thripitaka still intact I have a fourth also.

4. It should be in Thripitaka Buddha Deshana.

Buddha Deshana are in Pali (Pali text, Magadhi sounds), the translations are NOT Buddha Deshana, but again some theories/definitions by someone else!

Knowing very well that they are translations by say a person A, what is the point of trying to validate it with another person B’s?

Therefore we have to validate them with the original Pali. So this step is the most difficult. If you have Nirukthi Gnaana you can directly decode the Pali text and derive the meaning by just listening to the sound. But if you don't have that, you have to use the translations very carefully, keeping in mind that they are someone else’s opinions, and try to grasp the whole meaning in such a way that we adhere to the 1,2,3.

P.S.

If you read carefully you would ask what is 1,2,3 and how I came up with those three.

Well that is not my method, it is clearly stated by Lord Buddha as the method to validate dhamma if in doubt.

But then how do we validate if the validator is valid?

That you have to validate by another means.

This is by Prathyaksha Gnaana that must be gained only be first learning 1,2,3 from Lord Buddha or a person who has understood from him (an Arya), and then practicing it until you excel.
This is called "Para-tho-go-shaya" meaning sound from another person.  

There is no other way.