Perhaps the time quoted is what it takes for the consulate and the comune to communicate, transcribe and notify the applicant (with the child being an Italian citizen all along/since birth). It seems like a very long time.
I have not done it personally, perhaps someone can chime in. My understanding of the process is that the Italian citizen parent (previously registered in AIRE at the corresponding consulate) reports all relevant life events (i.e. birth of a child) to the AIRE via a consulate corresponding to his/her place of residence (or if living in Italy directly at the comune), by presenting the birth certificate apostiled and translated to Italian (only exception to apostile+translation is if the birth was recorded in the country signatory to the Vienna Convention, Argentina not being one of these). The transcription of the information received in the consulate is then done at the comune in Italy, and then the comune forwards the confirmation of transcription to the consulate and the Italian citizen parent is notified. At this time you may request a plurilingue IT birth certificate directly form the comune in IT.