Xanthorrhoea glauca subsp. angustifolia

In order to be certain of the ID to species level of Xanthorrhoeas you need to look at the bracts surrounding the flowers, and the bracts between the flowers. This is a job for a specialist in Xanthorrhoea.
I have based this ID on known records at Burrinjuck. Australis is the common species there. There are a few records of glauca from the 1050s.

X. australis is perhaps the most misunderstood taxa within the genus with various grass-tree species, not uncommonly, being misidentified as belonging to the Southern or Austral Grass-tree, probably because it is one of the most well-known.
X. glauca angustifolia is an almost identical species, other than genetical differences, what separates this taxon from X. australis is habitat, distribution and some very subtle morphological characteristics.
The geographical distribution X. australis was previously thought to be more widespread that what is now understood. Research undertaken and published in 2009 by (Bellete, M.P: The Biogeography and Ecology of Xanthorrhoea glauca subsp. angustifolia in South-eastern Australia.) highlighted that those populations once designated as X. australis occurring north of the DV in Victoria and west of the Range in NSW have actually been identified as belonging to the very similar-looking taxa, X. glauca angustifolia, a species that was once described as X. australis ‘eastern form’.
One of the most reliable means with which to separate the species is to observe and compare the packing-bract morphology over the flower spike. The mature packing-bracts of both species exhibit acute to triangular-shaped bracts, however X. glauca possess many non-mature bracts which are spathulate, X. australis flower spikes do not exhibit this characteristic.
X. australis niche tends to be the milder regions such as along the coastal fringes and along the eastern and southern aspects slopes and foothills of the Dividing Range. The inland locality of this specimen typically identifies with X. glauca angustifolia, a species better capable of tolerating the colder winter temperatures of inland tablelands.
The locality, the grass-trees at Burrinjuck would also have been misidentifications of X. australis and undoubtedly are X. glauca angustifolia based on updated information.

Thanks for your help with this genus @marcycad . I will try and get close ups of the flower spikes for ID in the future.