Australian Bureau of Statistics:
Q2: Is the data complete?
A: Occurrence data is incomplete because of a lag in registration. Each year, the ABS receives births data from each state and territory’s Registry of Births, Deaths and Marriages. This includes all births that occurred and were registered in Australia during the preceding year.
There is usually an interval between the occurrence and registration of a birth (referred to as a registration 'lag') and as a result, some births occurring in one year are not registered until the following year or later. This can be caused by either a delay by the parent(s) in submitting a completed form to the registry, or a delay by the registry in processing the birth. Births which occur in December are likely to be registered in the following year.
A: Due to a lag in registration, only 6,659 births that occurred in December 2021 were registered in 2021. Most of the remaining occurrences will be registered in the following year. Using 2019 and 2020 data as examples, the occurrences for December 2020 and 2019 were 6,683 and 7,655 but then increased drastically by the time the official Births, Australia report came out. At this point, the totals had reached 22,695 and 23,231.