Lawrence Officer states that Australia left the gold standard in 1930.
However, Barry Eichengreen stated that Australia left the gold standard
in December 1929.
Can you answer me which is the right answer (or even if, as was the case
with Canada, Australia left de facto the gold standard in december 1929
and formalised it in 1930).
The Answer
Eichengreen and Officer are consistent -- the year is 1930. Eichengreen (pp. 234-235) writes, after beginning the pgph with "In December 1929," that in "the following month" the Australian government required citizesn to deliver gold to the Commonwealth bank.
However, you raise a good point: what is the criterion for leaving the gold standard. The answer is not simple. Note that in Table 2 there are two steps to adopting the gold standard (exchange-rate stabilization and currency convertibility) but only one step to ending the standard (one ending date). Also, as the question observes, de jure and de facto could provide different dates. Officer's criterion is always (or, at least, should always be) de facto.
A final note, that has arisen in a private communication with another scholar, the sources for Table 2 are of varying reliability, in my view. The most reliable are the Federal Reserve Bulletin and League of Nations publications. The least reliable is Kemmerer.