The ṣ substitution does not take place in the s of sad and ṣvañj after the reduplicate in the liṭ (Perfect Tense).,
In the Perfect, when these words are reduplicated, there are two स's, as ससाद and सस्वंज ॥ After a preposition, the first स will be changed to ष, but not so the second. Thus अभिषसाद, परिषसाद, निषसाद, विषसाद, परिषस्वजेः, परिषस्वजाते, परिषस्वजिरे, अभिषस्वजे ॥ The nasal of स्वंज is elided though here, the लिट् affix is not कित्, because it ends in a compound vowel 6.4.24, 1.2.5 and 1.2.6.
The word स्वंज does not occur in the sutra, but has been inserted in it by the author of Kasika from the following Vartika:- सदो लिटि प्रतिषेधे स्वञ्जे रूपसंख्यानं कर्तव्यम् ॥,