Siddhas who are familiar with the secrets of upāsanā of Bhagavatī Durgā, point out the presence of navārṇa in two places within the Durgā Saptaśatī.
The name Chāmunḍā is of great significance, as is evident by it’s central position occupied within the famous Navārṇa mantra.
यस्माच्चण्डं च मुण्डं च गृहीत्वा त्वमुपागता ।
चामुण्डेति ततो लोके ख्याता देवी भविष्यसि ॥
yasmāccaṇḍaṁ ca muṇḍaṁ ca gr̥hītvā tvamupāgatā |
cāmuṇḍēti tatō lōkē khyātā dēvī bhaviṣyasi ||
The word ‘cāmuṇḍāyai’ is composed of nine letters – च्, म्, ण्, ड्, य् and आ, उ, आ, ऐ – and hence is nāvākṣarī in its own right. This very name is considered very powerful and a mantra in itself.
There is yet another powerhouse verse in Saptaśatī that is described as nāvārṇa by Siddhas of the yore:
शूलेन पाहि नो देवि पाहि खड्गेन चाम्बिके |
घण्टास्वनेन नः पाहि चापज्यानिःस्वनेन च ||
If one carefully observes, this verse contains the letter ‘na’ (न) nine times.