Read as a group, the four semivowels are the clearest demonstration that the varnamala is an analysis rather than a list. The grammarians identified four vowels, i, vocalic r, vocalic l and u, and observed that each has a consonantal counterpart made at the same place; they then placed those four counterparts together in the table, in the order of the vowels they answer to, between the stops and the sibilants. The class name they gave them, antahstha or standing between, states the analysis in a word. The rules that convert each vowel into its own semivowel before a dissimilar vowel follow directly, and so does the reverse process by which a semivowel becomes a vowel in certain grammatical formations.
Nothing about this is inherited from an older alphabet: it is a description of Sanskrit arrived at by examining Sanskrit. That is the difference between the varnamala and the Greek, Hebrew and Roman series covered elsewhere in this atlas, whose letters sit in an order transmitted from Phoenician and whose names are Semitic words for ox, house and camel. This atlas records for each semivowel its place, its articulation, and the vowel it answers to, and does not assign any of them a numerical or symbolic value, because the tradition does not assign one.