In the case of personal names, the choice of the etymology is often a matter of compliance with assumed phonological rules. Since the geographical aspect of the occurrence of sound changes (i.e. o > a) within Thracian territory, based on the work of V. Georgiev, began to be emphasised by some researchers, the chronological aspect has been somewhat neglected. There are numerous cases where lack of information has obscured the vocalism of these idioms, generating the most contradictory theories. Today, some 3,000 Thraco-Dacian lexical units are known. In the case of the oscillation *o / *a, the total number of words containing it is about 30, many more than the ones cited by both Georgiev and Russu, and the same explanation is not valid for all of them.