I understand the terms are used differently. That is, adjustable value is used for balancing adjustments and cost for the capital gains on the private use portion.
However, and importantly, tax deductions already obtained (in this case depreciation) reduce BOTH the cost/cost base of CGT assets as well as the taxable portion of the depreciating assets (adjustable value).
Your examples, take into account the 90% of dedications attributable to the taxable use portion, but do not take into account the 10% that is attributable to the private use portion.
if you were to take this into account, the cost would be reduced to 300 not 500. This is why I am confused by the ATO example.
As you can see in your examples, you only ever take into account 90% of the deductions or 1800.
What I am saying is the remaining 200 in deductions must be taken into account for the private use portion. Afterall, both specifically state deductions claimed are generally excluded from the cost and adjustable value.
The only explanation I can think of is that cars are excluded from this and you don't have to take into account dedications claimed.
