One could create a calendar using simply 12 months determined by the Molad. In fact, the Moslem’s calendar is based on just 12 lunar months. But such a calendar would not track the seasons as determined by the sun.
GUcHADZaT is the way this is accomplished in the Fixed Hebrew Calendar. GUcHADZaT is a mnemonic, gimel-vov-het aleph-daled-zayyen-tet, for a series of seven years, 3-6-8-11-14-17-19, in a 19 year cycle which are given an extra month of 30 days. This incorporates a principle originally attributed to Meton of Athens, in the 5th Century BCE, that 19 solar years are nearly equivelent to 235 lunar months.
There are 19 possible ways to make this distribution so it was amazing to find that the Babylonians were using the same series as we do to this day during the period 490 BCE to 312 BCE.
Since we now know that use of Molad began in 791 BCE and knowledge of the relation of 235 lunar month to 19 solar years could have existed then it is reasonable to assume that the Jews always used GUcHADZaT and thus the Babylonians adopted this Hebrew technology.