विंशत्यादिभ्यस्तमडन्यतरस्याम्

After the words विंशति etc. तमट् (तम feminine in ङीप्) is optionally the augment of डट्।
This rule falling under the jurisdiction of पूरण, we must read the word डट् into this sutra, as the affix to which the augment तमट् is added. Thus विंशतेः पूरणः = विंशतितमः or विंशः 'twentieth'. एकविंशतितमः or एकविंशः, त्रिविंशतितमः or त्रिविंशः, त्रिंशत्तमः or त्रिंशः, एकत्रिंशत्तमः or एकत्रिंशः ॥

There is no विंशत्यादि class given in Ganapatha. These are ordinary words like विंशति, त्रिंशत् &c. The words विंशति, त्रिंशत् &c of 5.1.59, should not be taken as the विंशत्यादि alluded to by this sutra. For had it been so, we could not have formed the words like एकविंशतितमः; because the rule applying to विंशति specifically mentioned, will not apply to विंशति as the end of a compound. As this maxim declares, ग्रहणवता प्रातिपदिकेन तदन्तविधिर्नास्ति "that which cannot possibly be anything but a Pratipadika, does, contrary to (1.1. 72); not denote that which ends with it, but it denotes only itself". This being the case, the word विंशति &c must be taken in their popular signification, and not as particular pratipadikas; and hence also becomes valid the exception given in 5.2.58, in the case of षष्टि &c when preceded by another numeral. For the very prohibition असंख्यादेः in that rule, shows, that with the exception of षष्टि &c, the present rule applies to other संख्यादि words, as, एकविंशति &c.

Bohtlingk takes मट्, थट् and तमट् as separate affixes and not as augment. He says "The commentators take तमट् here and in the following Sutras as an Augment of डट् 5.2.48, because विंशति &c with the affix तमट् would yield विंशतित꣡म by 3.1.3, whilst otherwise it would be accented as विंशतितम꣡ ॥ According to this interpretation मट् 5.2.49 and थट् 5.2.50 are Augments, though they would yield the right form as affixes also. That Panini by forms मट्, थट् and मयट् so much resembling डट्, should not have meant an affix, is not probable. Moreover one does not understand well this, why he, if he intended that म, थ and तम should be taken as augments, does not, for the sake of clearness, ordain this after the stem, which could have been expressed by adding of the servile क् (i. e. मुक्, थुक् and तमुक्), as he does in the case of the augments थुक् 5.2.51, तिथुक् 5.2.52 and इथुक् 5.2.53. I also think this, that Panini, when he designated this affix तमट्, did not think of the accent."

In the case of मट् and थट् there will be no difference whatever whether we take them as affixes or as augments. Thus पंचन् + मट् = पंच् + मट् 6.4.144 = पंचम ॥