Ancient Indian sources describe each of the four Vedas as having once existed in a considerable number of distinct shakhas, branches, each maintained by its own lineage of Brahmin reciters with its own precise oral text and, frequently, its own associated ritual and interpretive literature, so that a shakha was never simply a copy of the same text but a whole transmitted tradition built around it. Only a small fraction of these once numerous branches survive today in active oral transmission, among them the Shakala recension of the Rigveda, the Kauthuma and Jaiminiya recensions of the Samaveda, and, within the Yajurveda, branches including the Taittiriya, Madhyandina and Kanva traditions, each preserved by specific communities, often concentrated in particular regions of India, that have continued training reciters in that branch's exact oral form across many generations.
The reasons for this drastic narrowing from a much larger original number are partly a matter of straightforward loss, as small, geographically limited reciter lineages died out without successors, and partly a matter of some traditions proving more resilient than others, better supported institutionally or more central to widely performed rituals, and so more likely to be actively maintained rather than allowed to lapse.