I have the Scott 2007 catalogue with the Australian prefix and it has the Australian State stamps first,I believe it's because the state stamps started in 1850 to 1913,with Federation of the states in 1901 an Australian stamp went into circulation in 1913 (roo stamp)this is why I think Scott catalogue will always start with the Aussie states first so that's the way I think they should be collected but that is just my opinion.
regards Harry
