It's even worse than you describe Robin,

The basic topo map scale in all of Oz is 1:25,000; although surveying data are collected at that scale the maps issued will be at 1:25,000 only in those areas where our political masters have agreed they'll get a financial return on their printing. This means only coasts in Qld, as far inland as the Great Dividing Range for most of NSW and Vic. (not sure about other states). 1:50k is common in some parts of Vic and NSW but the scale used by natural resources people (botanists and geologists, mostly) seems to be 1:100k. Aircraft routinely use Joint Operations Graphic maps at 1:250k; as you might have guessed, no matter which scale I choose, my place is right at the junction of four sheets.

Back to the story.

When surveyors from National Mapping were compiling data for western Queensland they realised that the 19kV powerlines were a major feature in an otherwise relatively featureless landscape and so recorded their locations carefully. But the wally-in-charge decreed that no powerlines were to be printed on maps unless they were 20kV or above. So the major navigation feature for western Queensland was deliberatley left off the maps available to the public.

And I do recall someone trying to use a GPS in western Queensland with the datum set (unknowingly; and it wasn't me) to a more recent geoid than the one used by the surveyors, meaning locations findable from the two sources (map and GPS) were about a km apart; very tricky!

Cheers, Rowan