The Chinese translations show that there were a number of Indian Vinaya collections available in the fifth century, some of which were also later available to the Tibetans (remembering for example that Atiśa [980-1054] was in the Mahāsāṅghika system). The Tibetans had contacts with the Chinese Buddhists in the seventh to eleventh centuries, and they did indeed translate a number of Chinese Buddhist texts, but they did not in general consider Chinese translations as sources for the Tibetan Buddhist canon, disregarding the extensive corpus of Vinaya materials in Chinese.9 This is made evident by the fact that the Chinese translated at least five Vinayas, four in the early fifth century,10 and a number of texts of Mūlasarvāstivādin in the late seventh or very early eighth century, by Yijing (ca. 635-713), all of which went unrecognized by the Tibetans.
There is also no evidence that Guṇaprabha’s texts were translated into Chinese. Given their importance in Tibet, and presumably in India, the absence of Guṇaprabha’s Vinayasūtra texts, like some philosophical texts (of Candrakīrti [fl. 600-650], Dharmakīrti, and others, for example) is odd, but might be merely a matter of timing. Davidson suggests that the majority of Chinese pilgrims visited India before the development of those religious movements and that the philosophical and monastic texts not included in the Chinese canons had not yet been composed or at least not widely circulated.11 Otherwise, if there was a later stream of Chinese pilgrims, the lack of these materials in Chinese was a matter of [page 5] accessibility, or because they were overlooked or ignored by the Chinese pilgrims and translators.
The Tibetans only translated the Mūlasarvāstivāda Vinaya, the longest Vinaya, in the eighth century, and Guṇaprabha’s summary texts later. The early translation signals the Imperial adoption and later eastern Tibetan monastic preservation of the Mūlasarvāstivāda system. The subsequent Tibetan choice of the Mūlasarvāstivāda and later works by Guṇaprabha may have been a matter of sectarian popularity of that system in eastern Tibet and in India, to the intentional exclusion of other Indian systems and of the extensive Vinaya collections in Chinese. If so, the Tibetan exclusive translation and adoption of Mūlasarvāstivāda and derived texts makes sense, and marks a consensus among Tibetan religious authorities.
Alternatively, was the Tibetan adoption of Mūlasarvāstivāda-derived texts more by circumstance, merely a matter of availability of canonical texts made popular in the places where they acquired their materials, less a matter of sectarian consensus among Tibetans? Frauwallner speculated that different Vinaya systems were based on the realities of distance between Buddhist missions, which may have had earlier common sources but over time developed monastic and doctrinal differences.12 If this was the case, the Tibetan selection of the Mūlasarvāstivāda and later Guṇaprabha’s corpus was not at all a conscious religious or doctrinal choice, but merely a matter of regional availability. The source places for early Tibetan Buddhist materials are generally known, for example, Nepal, Kashmir, and Bengal, but if regional availability was a determining factor, it indicates that Tibetan Buddhists were adopting a specific regional system or systems piecemeal, and not at all comparing, collating, or fully editing materials from a pan-Indian Buddhist tradition. This means that the choice of Mūlasarvāstivāda was not as much of a choice as a matter of chance.
In support of this, regional Vinaya traditions in India are noted by Frauwallner, who wrote that in addition to the Pāli Vinaya in Śrī Laṅkā, “[t]he Vinaya of the Mūlasarvāstivādin would be the Vinaya of Mathurā, and that of the Sarvāstivādin the Vinaya of Kaśmīr …and Gandhāra.” He further notes that “the earliest translators of Vinaya texts of the Dharmaguptaka into Chinese were the Sogdian K’ang Seng-k’ai and the Parthian T’an-ti,”13 and Dutt speculates that the Mahāsāṅghika were based in Mathurā or Kaśmīr.14 These scholars make a case for the Mūlasarvāstivāda and possibly the Mahāsāṅghika Vinaya being current in the places Tibetan translators searched for canonical documents. This argument is further corroborated somewhat by the facts that Guṇaprabha’s legendary home was Mathurā, and his important Autocommentary is also known as the “Mathurā [page 6] Commentary.”15 The choice or rather chance adoption of Mūlasarvāstivāda and Guṇaprabha might indicate the prominence of Mathurā over Kaśmīr and Bengal as a primary source place for the Tibetan Vinaya, even in light of the well known importance of these latter sites in Tibetan Buddhist history.
 See the early lists of Chinese texts translated into Tibetan in Georgios Halkias, “Tibetan Buddhism Registered: A Catalogue from the Imperial Court of ’phang thang,” The Eastern Buddhist 36, nos. 1-2 (2004): 66, 99-100.
 E. Frauwallner, The Earliest Vinaya and the Beginnings of Buddhist Literature (Rome: Serie Orientale Roma, 1956), 1-2 lists the Vinayas in Chinese translations: “the Sarvāstivādin, Dharmaguptaka, Mahīśāsaka, Mahāsāṅghika, [and the] …Mūlasarvāstivādin.” See Jan Nattier, A Guide to the Earliest Chinese Buddhist Translations: Texts from the Eastern Han and Three Kingdoms Periods (Tokyo: The International Research Institute for Advanced Buddhology, Soka University, 2008), 3.
 Davidson, Tibetan Renaissance, 125.
 Frauwallner, Earliest Vinaya, 12. See Nalinaksha Dutt, The Early History of the Spread of Buddhism and the Buddhist Schools (New Delhi: Rajesh Publications, 1980), 110-123.
 Frauwallner, Earliest Vinaya, 1-23, 37 ff.
 Dutt, The Early History, 132-136.
 ’Dul ba’i mdo’i ’grel pa bcom brlag ma zhes bya ba [[[Wikipedia:Mathurā|Mathurā]] Commentary] (Guṇaprabha, ’Dul ba’i mdo’i ’grel pa mngon par brjod pa rang gi rnam par bshad pa, 273b.5).