Back in 2017, Betty Wood made the comment that "The name Xanthorrhoea australis in the ACT is now considered to be a misapplication. That species was dropped from the ACT Plant Census (2017)." and was always pretty adamant that there was only one species of Xanthorrhoea in the ACT. I have always found it difficult to distinguish grass tree species and have followed Betty's advice. Are you sure this is X. australis rather than glauca? If it is australis then the glauca records would need to be checked.