The Australian system renews at the renewal date if the medical is completed within 28 days prior to the renewal date (see previous post).
ICAO renews from the actual date of the medical. (ie medical done on 1st June, 6 months would be 1 December, 12 months would be 1 June of the next year)
Therefore, if an Australian licence holder was to operate outside of Australia, beyond the 6 month period (or 12 months as the case may be) from the actual medical renewal date, then the medical would NOT be valid from an ICAO perspective.
I think this is correct.