A unique amalgam of fascinating potentials enabled the usage of phase change materials in rewritable optical and electrical storage technology. Furthermore, the identification of stoichiometric tuning of disorder in these materials opened up new pathways for the selection of materials for multi-bit data storage. Despite a reasonable understanding of structure and properties, an in situ study could aid in unravelling vital insights. Hence, we report on an analogy between the degree of disorder in Ge₁Sb₂Te₄ and Ge₂Sb₂Te₅ materials by employing novel temperature-dependent correlations of optical band gap (E_g), Tauc parameter (measure of disorder, B^1/2 slope) and the change in band tail. E_g decreases from 0.8 eV (90 K) to 0.34 eV (480 K) for Ge₁Sb₂Te₄ and from 0.82 eV (90 K) to 0.36 eV (480 K) for Ge₂Sb₂Te₅. This trend reveals the semiconducting nature of both amorphous and crystalline phases. The change in disorder as exemplified by an increase in B^1/2 of 2.7% and 14.9% during the phase transition of Ge₁Sb₂Te₄ and Ge₂Sb₂Te₅ respectively reveals a stronger degree of disorder in the cubic phase of Ge₁Sb₂Te₄ as compared to the cubic phase of Ge₂Sb₂Te₅. These findings are strongly supported by an unambiguous change in the width of the band tail. This confirms the origin of a pronounced disorder-induced localization in Ge₁Sb₂Te₄ compared to the Ge₂Sb₂Te₅ material.