As I have been reading the Lipiśālāsandarśana-Parivarta [p. 89, P. L. Vaidya edition], some interesting features of the alphabet popped up for me.  The Alphabet omits r̥ and l̥, but includes ai, au, and aḥ. Among the consonants, it adds kṣ at the end after h.  The version of this passage as given in the Bauddhāgamārthasaṅgraha [ed by P. L. Vaidya] also omits l, while it is included in the version of Lalitavistara edited by Vaidya himself.  I wonder if there are textual variants about this.  I don't know what this alphabet represents.  The omission of r̥ and l̥ goes along the phonologies of Prakrits, but the inclusion of ai, au, and aḥ goes in the direction of Sanskrit.  The addition of kṣ and the possible omission of l point to something else that I cannot figure out.  Any suggestions and references are welcome.