Vedic literature constitutes of four Vedas, 108 Upanishads, Itihasas like Mahabharat & Ramayan, 18 Puranas, Smrities etc. We learn about the truth by reading these literatures.
In this age of kali, there is rampant interpolation in the Vedic scriptures. In these circumstances, how shall we judge the authenticity of a particular Vedic literature ? As every Sampraday has it's own version of a particular scripture and consider it as genuine.