Georgiev and Duridanov argue that the phonetic divergences above prove that the Dacian and Thracian (and Phrygian, per Georgiev) languages could not have descended from the same branch of Indo-European, but must have constituted separate, stand-alone branches. However, the validity of this conclusion has been challenged due to a fundamental weakness in the source-material for sound-change reconstruction. Since the ancient Balkan languages never developed their own alphabets, ancient Balkan linguistic elements (mainly placenames and personal names) are known only through their Greek or Latin transcripts. These may not accurately reproduce the indigenous sounds e.g. Greek and Latin had no dedicated graphic signs for phonemes such as č, ġ, ž, š and others. Thus, if a Thracian or Dacian word contained such a phoneme, a Greek or Latin transcript would not represent it accurately. Because of this, there are divergent and even contradictory assumptions for the phonological structure and development of the Dacian and Thracian languages. This can be seen from the different sound-changes proposed by Georgiev and Duridanov, reproduced above, even though these scholars agree that Thracian and Dacian were different languages. Also, some sound-changes proposed by Georgiev have been disputed e.g. that IE *T (tenuis) became Thracian TA (tenuis aspiratae), and *M (mediae) = T: it has been argued that in both languages IE *MA (mediae aspiratae) fused into M and that *T remained unchanged. Georgiev's claim that IE *o mutated into a in Thracian, has been disputed by Russu.