Why do we still don't know exact birth & date year of the Buddha? I just want to know:
1)Why do we still don't know exact birth &amp; date year of the Buddha?
2)What are the factors that is limiting in knowing Buddha's birth &amp; death year?
3)Why many people/countries/traditions contradict? Many countries following different traditions, follow different Buddhist calendar year i.e. years since Buddha left. 
4)Even the recent Nat Geo Excavations reveal he might be born in 6th Century B.C. A 2013 news which still doesn't official claim nor does it leave a convincing conclusion till date, on whether their findings are indeed perfect or not. Nor their findings seems to be accepted if its true.
5)Does the pali text gives any reference to the same?
Knowing the precise date of the Buddha's birth is not very useful knowledge within the Buddha's teaching, as it is presented in the Pali Suttas. How will knowing this precise birthday help any student transcend their own suffering? Only the most worldly and materialistic forces within any tradition would care about such superficial things.

The Pali Suttas(and arguably the Sanskrit Sutras) are the closest to what the Buddha actually taught. All traditions derive their truth from the Suttas/Sutras and other truths that might or might not be so compatible with the Buddha's actual original teaching. These additions were made for reasons of culture, politics and practicality IMHO.

If one wants to know what was likely the truth that the Buddha taught then one might stick to the core teachings that the Buddha repeated over and over again in the Suttas/Sutras. 

It seems to me that these core teachings fit within themselves with great precision. Their potential is so awe inspiring to me that I wonder what, in 2500 years, has been stopping so much of humanity from embracing the Buddha's teaching or any teaching like the Buddha's teaching.-Metta :)