A few years ago I researched the female convicts from the ship Elizabeth
which arrived in January 1828.
During that research I found that many hundreds of BDM entries were recorded
in the church records but were never transcribed.
I even found some entries post 1856. I am sure no-one would know the extent
of the missed entries.
SAG and the Mitchell Library filmed a large number of the church registers
and copies can be found at either place.
It was tedious task because you need to go through each reel line by line.
Also many religious events never took place or much later than the expected
date or again the clergy lost the little bits of paper that he carried from
place to place.