In 2004 the Royal Australian Mint began transitioning to computerised engraving of dies. For most denominations the new technology was used from 2005 onwards but the 2004 20c was produced using both old and new technologies (p128, McDonald, Pocket Guide to Australian Coins and Banknotes, 2017).
The old-style coins have a larger portrait with pointed top A's in the legend (so-called big head coins) and the new-style coins have a smaller portrait with flat top A's in the legend (so-called small head coins). Most circulating coins are small head coins with large head coins making up about 1.2% of the total mintage. Most or all mint and baby sets are large head coins and proof sets contain both large head and small head coins though the proportions are unknown.
Mint sets were not produced in all years of decimal Fijian coinage. In most years that mint sets were produced, the mint that produced the circulating coinage also produced the mint sets. Although catalogues say that circulating coins dated 1983 were produced, 1983 was a mint set only year, and in 1984 only circulating 1c and 2c pieces were struck, both by the Royal Australian Mint. Mint sets in 1983 and 1984 were both produced by the Singapore Mint, with 3,000 sets struck in 1983 and 5,000 sets struck in 1984.
The Singapore Mint-struck coins do not bear any mint marks or distinguishing marks but they can be distinguished from their circulating counterparts. On the Singapore Mint-struck coins the Queen's hair has shallower incuse lines, the legend lettering is thinner and the tip of the Queen's tiara is closer to the rim.
In the middle of 2018 two reported 2015 mule dollars were sold on ebay by a user listing their location as Canberra. Both listings had the same images and the auctions finished on June 27th with a final bid of $711 and July 17th with a final bid of $760. Both sales resulted in positive feedback for the seller.
The next sale of a 2015 mule dollar occurred as lot 126 in session 1 (July 21st 2018) of Noble Numismatics sale 118 where it sold for $2,000 against a $2,000 dollar estimate. It is unclear if this coin was one of the two earlier examples.
The circumstances in which the coins were struck is unclear but the prevailing attitude is that they were deliberate fabrications by mint staff. Their sale by a person in Canberra is not conclusive but contributes to that theory.
In 1992 the Royal Australian Mint struck 50c pieces for the Cook Islands. Most of the 50c pieces struck used the new turtle reverse design by Horst Hahne which had been introduced in 1988. For unknown reasons a small number of 50c pieces were also struck using the old bonito fish reverse design by James Berry, which had last been used in 1987.
The re-use of the old dies was limited - from a sample it appears that about 7.7% of 50c pieces struck used the old design.
In the early 2010s it was noticed that a small number of 2008 Australian 20c pieces had a small gap between the wave and the playtpus' head, similar to the wave gap used as a mintmark on 1966 20c pieces. While it is a part of the design that is subject to die fill, it was realised that it was likely a genuine variety as the 2008 Wedding Set coins all exhibited the wave gap. With a mintage of just 3,278 sets, the wave gap was unlikely to be due to die fill. It seems likely that the Royal Australian Mint accidentally deployed a Wedding Set reverse die for the production of circulation coins, though it is unclear why such a design change was made for the Wedding Set coins.
2008 20c circulation break-downs
While the wave gap variety makes up a very small percentage of the total mintage, with 132,900,000 2008 20c pieces struck, there were approximately 1,000,000 wave gap coins struck.