Studies on the Issyk and Ay Khanum inscriptions, dated to the 5th-4th centuries BC, have historically relied on the linguistic norms of 8th-century AD Orkhon Turkic (Standard/Shaz Group), leading to significant chronological and phonetic inconsistencies. Saltaoğlu and Güneri (2022) recently proposed that these texts should be deciphered using "Pre-Turkic" phonetics. While building upon this proposal, this study introduces a novel methodological approach to fill the existing analytical gap: "Back-Reconstruction via Isolated Dialects." The study employs the "Weighted Phonetic Concordance Model" (WPCM), developed by referencing the phonetic characteristics of the most archaic and isolated branches of the Turkic language family: Oghur (Chuvash), Argu (Khalaj), and Siberian (Yakut). Based on principles of lexicostatistics and quantitative linguistics, the analysis reveals that while the probability of explaining the inscriptions through Standard Turkic is merely 8.3%, the probability of explaining them through the Proto-Forms of Isolated Dialects is 92.5%. These data mathematically demonstrate that the inscriptions belong to the Early Pre-Turkic period, preserving distinct Lir-Turkic and Argu characteristics.