As you suggest, the current legislation is intended to be consistent under an election scenario. When Parliament is dissolved, there are no committees for the PBO to report to. The expectation, as the legislation is currently drafted, is that should a party wish to have an election platform costing done, the PBO would have resources freed up in order to do that. I think it's consistent with your commentary around the caretaker convention.
On May 29th, 2017. See this statement in context.