Many past figures(statistics) that are available are gleaned from the people attending registered gender clinics and do not take into account those who chose not to present for medical assessment, or in some cases, have declined surgery.

The process of transition and changing gender has been socially secretive. This has made the availability of patient records difficult to assess and obtain.

Research done by Lynne Conway- Professor of Electrical Engineering and Computer Science, Emerita University of Michigan, Anne Arbor, MI, Electrical Engineer, Inventor, Research Manager, Engineering Educator, Grandmother, and Transsexual woman(reassignment surgery in 1968) revealed that in the US male population, aged 18-60, prevalence of transsexuality is as high as 1:625 or 1:500.

This was backed up by the following figures:

In 1973 that Dr Benjamin's records showed that at least 2500 TS women in the US were post-op by that date.
That since 1990 about 800-1000 reassignment surgeries for M to F(Male to Female) transsexuals had been completed each year in the US.
Surgeon Stanley Biber has done over 4500 GR surgeries since 1969.
The 1993 CIA report on Sexual Behaviour and Security Risk: Background Information for Security Personnel concluded that: males who live as women are accepted in a variety of cultures, including India, Burma, Oman, Polynesia and North American Indian tribes. In one small town in Oman where they were studied, the Xanith, as they are known there, comprised 2% of the 3,000 adult males.(1:50 males or, assuming roughly equal numbers of males and females, 1:100 of the towns population.)
There being at least 1:9000 post-op women in Australia and, allowing for a conservative estimate of two-thirds of all Australian TS women being pre-op, non-op or still closeted (US and UK figures show four-fifths), the true prevalence could be 1:3000 of the total population and as high as 1:1000 among the adult male population.

It appears that there are many more transgendered people in the population than commonly believed, and that medical professionals and Ministries are still working with outdated statistics and figures.
It could be construed that Medical professionals and Ministries using antiquated data could lead to discrimination or bias against the TS and TG sectors in Australian society.