As I have seen in rigveda and gita, only three Vedas are referred but yajurveda defines of four Vedas, so it is same as people say that there has been some addition etc.in mahabharat and other scriptures also . But as defined by ST.Augustle in Brief history of time by Stephon hawkin , the Ice age is assumed 10000 yrs. Bce . and the creation of universe at that time, our Vedas are also so old, hence I assume Vedas to be Apaurusheya [ not prepared by man ].Therefore Vedas can be considered to be the basic hindu scripture .Any explanation which is made by man in accordance with Vedas , but in hindu social boundaries is called vedantas and above social boundaries but taking Prakriti or nature in convention is called Vedastra: . Gita explains both vedantas and vedastras. According to gita the universe is made of two type of prakriti 1. jad prakriti and 2. chetan prakriti . Parmatma is the main cause of creation and destruction….. Bhoomiraapo’nalo vaayuh kham mano buddhireva cha; Ahamkaara iteeyam me bhinnaa prakritirashtadhaa. Earth, water, fire, air, ether, mind, intellect and egoism—thus is My Nature divided eightfold. Apareyamitastwanyaam prakritim viddhi me paraam; Jeevabhootaam mahaabaaho yayedam dhaaryate jagat. . This is the inferior Prakriti, Omighty-armed (Arjuna)! Know thou as different from it My higher Prakriti (Nature), the very life-element by which this world is upheld. Etadyoneeni bhootaani sarvaaneetyupadhaaraya; Aham kritsnasya jagatah prabhavah pralayastathaa. Know that these two (My higher and lower Natures) are the womb of all beings. So, I am the source and dissolution of the whole universe. Now see that the sourse is the universe and there are souls , but this has the limited boundaries, if you go on adding from 1 to millions the total remains limited, therefore there is no question of Moksha of atmas, gita confirms life after death and in bet. Atmas remain in universe . If we take the case of parmatma as in above shloka parmatma exists even when universe is dissolved also, but limit exeeds the universe and it is unlimited and the atmas are freed or Moksha is attained. Veda says..Vishnoryat parmam padam .