Different terms with the same meaning

It seems to me that between such a Vedic or Vedantic principle as नेति नेति (neti-neti – «neither this nor that») has much in common with द्वैताद्वैत विलक्षण (dvaitādvaita vilakṣaṇa) in the Nātha Tradition. The second is often found in the Sanskrit texts of Nāthas. In the later Nātha text in Hindi, Gorakh Sabadi, this principle is represented as अलख (alakh) – from the Sanskrit अलक्ष अ-लक्ष (a-lakṣa, i.e. «transcendence beyond the limits of symbols»).

What does it mean to be beyond duality and non-duality according to the Nātha doctrine?

Haṭhayogapradīpikā says:

अन्तर्लक्ष्यविलीनचित्तपवनो योगी यदा वर्तते
दृष्ट्या निश्चलतारया बहिरधः पश्यन्नपश्यन्नपि ।
मुद्रेयं खलु शाम्भवी भवति सा लब्धा प्रसादाद्गुरोः
शून्याशून्यविलक्षणं स्फुरति तत्तत्त्वं पदं शाम्भवम् ॥ ३७ ॥

antarlakṣyavilīnacittapavano yogī yadā vartate
dṛṣṭyā niścalatārayā bahiradhaḥ paśyannapaśyannapi |
mudreyaṁ khalu śāmbhavī bhavati sā labdhā prasādādguroḥ
śūnyāśūnyavilakṣaṇaṁ sphurati tattattvaṁ padaṁ śāmbhavam || 37 ||

By the grace of the Guru, when the consciousness and energy of Yogī are absorbed by the inner aim, perception (vision) is directed to the outside and motionless, but at the same time, suspended from vision; this mudrā known as śāmbhavī. That radiant essence beyond (vilakṣaṇam) of emptiness (śūnya) or fullness (aśūnya), is known as the Śambhū state (Śiva or the embodiment of appeasement).

Thuse, according to the Nātha Yogīs doctrine, to be beyond emptiness or fullness – means to be both emptiness and fullness simultaneously.