The four Vedas - Rig, Yajur, Sama, and Atharva - are the primary sources of information about Aryan history, culture, religion, and social structure. While Sama Veda is indeed a Veda, the question asks which is 'not one of the main sources,' implying it's less historical compared to Rig Veda, which contains more historical information about early Aryan society and their compositions.