Kishino Ryōji (岸野亮示) has written a useful monograph on the obscure topic of the brahmacaryopasthāna-saṁvṛti, a procedure in the ordination of nuns in the Mulasarvastivada Vinaya.
Essentially, women who ordain as nuns in Mulasarvastivada have a simple procedure that is outlined as a preliminary in their ordination. I made a few remarks about this in my Bhikkhuni Vinaya Studies, as a result of which Ryōji was kind enough to send me a copy of his monograph.
The nature and significance of the procedure is far from clear. I suggested that it may be a relic of an earlier ordination procedure done by nuns only, a procedure known in Pali by the related term vuṭṭhāna.
Be that as it may, Ryōji’s work focusses on the significance of the last element of the term, saṁvṛti (Pali sammuti). This refers to an “agreement” or “consensus” made by the Sangha.
Within the Tibetan traditions, it is sometimes assumed that this procedure is a requirement of a successful ordination. This is an problem, for the brahmacaryopasthāna-saṁvṛti is not a requirement in the Dharmaguptaka tradition, and hence it can be argued that Dharmaguptaka bhikkhuni ordinations are invalid to the Mulasarvastivada.
However, there are many requirements in the ordination procedures for both men and women that, if broken, may incur some penalty for those performing the ordination, but do not invalidate the ordination. Ryōji argues that the brahmacaryopasthāna-saṁvṛti is an example of such a procedure, hence its performance or lack thereof is not decisive in determining whether an ordination is legally valid.
While I haven’t reviewed all the texts in detail, his argument is careful and appears well-founded.
Along the way, he notes that I treated the Chinese term 本法 (basic dharma) as meaning upasthāna, whereas it more likely stands for upasthāna-saṁvṛti. I apologize for the mistake, and will correct it in future editions. However it remains unclear to me as how either of these terms came to be translated as 本法. And I note that even the highly comprehensive Digital Dictionary of Buddhism doesn’t include any relevant meaning for this term.