The number thirty-five is not incidental to Gurmukhi; it is the name of the alphabet. Painti is the Punjabi word for thirty-five, and to speak of the painti is to speak of the letters as a fixed and complete set rather than as a list that might grow. That has shaped how the script has handled everything added since. The six dotted letters for Perso-Arabic and English sounds were not folded into the alphabet and renumbered; they were kept outside it, taught separately, and described as extensions, so that the painti remains thirty-five and the additions remain visibly additional. The same is true of the vowel signs, the nasal marks and the digits, none of which is counted among the letters. A script that named itself by its count committed itself to a boundary, and the boundary has held for as long as the name has.
Ṛaṛa is the letter that marks it. Nothing about the sound it writes gives it that role, and it holds the last place for reasons of inherited ordering rather than of importance, but the effect is that the closing of the alphabet is a definite event: a learner reciting the painti knows exactly where it ends, and so does everyone listening.
A further consequence follows for cataloguing. The painti is thirty-five letters and the extensions are not part of it, so a count of Gurmukhi characters depends on what is being asked. A reference work that lists thirty-five is describing the alphabet as the tradition names it; one that lists forty-one is including the dotted letters; one that counts encoded characters is including the vowel signs, the nasal marks, the digits and several signs used only in the scripture. None is wrong and they are not interchangeable. This atlas holds the thirty-five and records the extensions on the letters they are built from.