The augment iṭ is added to the Participial affixes ta and tavat after kuṣ when it is preceded by nir,
As निष्कुषितवान्, निष्कुषितः ॥ The special mention of इट् in the sutra is for the sake of making its addition invariable, otherwise it would have been
optional, or debarred by 7.2.15. In the subsequent sutra, the addition becomes again optional.,