2004 Australian 50 cent varieties
In the early 2000s the Royal Australian Mint began using computerised engraving machines to produce coin dies - while 2004 is the reported year of the transition (p128, McDonald, Pocket Guide to Australian Coins and Banknotes, 2017), it is more likely that the change happened late in 2003 when production of 2004 mint sets was underway. For most denominations the transition happened with the year on the coins, though the 2004 50c piece was struck with both hand-engraved and computer-engraved obverse dies.
It is easy to distinguish the older hand-engraved die coins from the newer computer-engraved die coins - the old obverse die has pointed top As while the new obverse die has flat top As.
For the Coat of Arms reverse coins it is believed that all mint set coins were struck with the old obverse die and all circulation coins were struck with the new obverse die (p140, McDonald, Pocket Guide to Australian Coins and Banknotes, 2017), and a survey of circulating Coat of Arms 2004 50c pieces by the author affirms this. For the primary school designed animal reverse coins it is believed that all coins were struck with the new obverse die (p140, McDonald, Pocket Guide to Australian Coins and Banknotes, 2017) and a survey of circulating animal 2004 50c pieces by the author also affirms this. There is a possibility that some mint packaged/carded examples of the primary school animal 50c piece were struck using the old obverse though none have been reported.