Many phonetic features cannot be ascribed with certainty to a particular stage since there may be more than one possibility. Every phonetic form that can be ascribed to the Sasanian archetype on the basis of critical assessment of the manuscript evidence must have gone through the stages mentioned above so that "Old Avestan" and "Young Avestan" really mean no more than "Old Avestan and Young Avestan of the Sasanian period".
many phonetic features cannot be ascribed with certainty to a particular stage since there may be more than one possibility every phonetic form that can be ascribed to the sasanian archetype on the basis of critical assessment of the manuscript evidence must have gone through the stages mentioned above so that "old avestan" and "young avestan" really mean no more than "old avestan and young avestan of the sasanian period"