In 1921 the Melbourne Mint struck 7,378,073 threepences. Part-way through production the M mintmark ceased to be used, so 1921 Melbourne threepences are known both with and without the mintmark M below the date.
The reason for the phasing out of the mintmark is likely due to a decision made in 1919 - in that year, the Sydney mint was to begin striking halfpennies, and at the request of the treasury, dies were to not carry a mintmark so that they could be used interchangeably between the Sydney and Melbourne mints (p6, Sharples, Australian Coins 1919 to 1924 in Journal of the Numismatic Association of Australia, July 1985).
Two surveys on the frequency of both varieties were done by Briggs - in the first survey of 1921-dated threepences there were 83 with the mintmark and 17 without. In the second survey there were 85 with the mintmark and 15 without (p195, Briggs, Australian Silver Based Coinage 1910 - 1964, 2014). This suggests that around 84% of the mintage was struck using dies with the M mintmark and the remaining 16% with dies without the M mintmark, so while the no-mintmark coins are much less common they are not rare.
The Ian Rank-Broadley obverse underwent a number of changes during its use on Australian decimal coins. One of the more obvious changes was the change to the spacing of the initials IRB in 2001.
The 2001 $1 coin was struck with two obverse designs. On the first the initials IRB under the Queen's neck are spaced and in a sans serif font. On the second the initials IRB under the Queen's neck are joined and in a serif font.
A number of different $1 were produced in 2001 - the Centenary of Federation design which circulated; the Volunteers design which circulated; the Australian Army anniversary design which did not circulate; the Australian Navy anniversary design which did not circulate and the Australian Air Force anniversary design which did not circulate.
Among the circulating designs, the IRB joined obverse appears to have been used on all circulating Centenary of Federation and Volunteer coins. The IRB spaced obverse is also known on Centenary of Federation coins in mint sets, but it probably was not used for circulating coin. The author has found an IRB spaced Centenary of Federation coin in circulation though it is possibly from a set.
Among the non-circulating designs, the Australian Army anniversary, the Australian Navy anniversary and the Australian Air Force anniversary coins are all known with the IRB joined design. McDonald reports that Australian Army anniversary coins are also known with the IRB spaced design (p172, McDonald, Pocket Guide to Australian Coins and Banknotes, 2017) though it is the less common variety.
Most 2001 Australian $1 were struck with the IRB joined obverse so it seems that the IRB spaced obverse had a very short life - probably being phased out in 2000 during mint set production.
The George VI silver threepence was struck with two very similar reverse dies between 1937 and 1945: the main difference appears to be orientation of the I in IMP in relation to the rim denticles. On Davies reverse A the I in IMP points at a rim denticles and on Davies reverse B the I in IMP points between rim denticles (p99, Davies, British Silver Coins Since 1816, 1982).
In 1982 Davies reported that both reverse A and B were used to strike 1937 threepences though notes that the usage of reverse B is unconfirmed (p100, Davies, British Silver Coins Since 1816, 1982). In 2010 Groom repeated Davies' observation that the variety was unconfirmed (p104, Groom, The Identification of British 20th Century Silver Coin Varieties, 2010).
It seems unlikely that the 1937 reverse B silver threepence (Davies 2231) exists - the lack of any reported examples between the publication of two books on the series, and the lack of any attributed examples at auction suggest it will probably remain unconfirmed.
Although gold coins stopped circulating in Australia during World War I, the Melbourne Mint continued to strike gold sovereigns - by the late 1920s the mintages were low and by 1931 when the last sovereign was struck, the mintages were even lower. 1932 marked the end of sovereign production throughout the British empire, with only the Pretoria Mint striking sovereigns in that year. Like the Perth Mint though, the Melbourne Mint also received 1932-dated sovereign dies, though neither mint are known to have struck any 1932-dated sovereigns. In 1932 the Melbourne Mint received seven 1932 sovereign reverse dies (p48, Mullett, Gold Coinage and Refining at the Melbourne Mint, 1992), but the Melbourne Mint also received seven 1933 sovereign reverse dies in 1933 (p48, Mullett, Gold Coinage and Refining at the Melbourne Mint, 1992). While the receipt of 1932-dated sovereign dies is not surprising - they were prepared and sent to the other two mints that had produced sovereigns in 1931 - the receipt of 1933-dated sovereign dies is surprising, as Great Britain had abandoned the gold standard in 1931, and the Melbourne Mint had not struck any sovereigns after 1931.
The Melbourne Mint received 1934-dated sovereign dies in 1934 as well, though on this occasion only four dies were received (p48, Mullett, Gold Coinage and Refining at the Melbourne Mint, 1992). The reason for 1934-dated sovereign dies is known however: the Melbourne Mint had specifically requested them to strike sovereigns for the centenary of the state of Victoria in 1934 (Eigner, https://www.drakesterling.com/news-wire/post/the-1934-melbourne-sovereign). While the Royal Mint was reluctant to have sovereigns struck, it was conceded that laws still required sovereigns to be struck on demand (perhaps explaining the production of 1933-dated sovereign reverse dies). The Melbourne Mint confirmed receipt of the four dies on 26th April 1934 (Eigner, https://www.drakesterling.com/news-wire/post/the-1934-melbourne-sovereign). There are conflicting reports of when the dies were destroyed - according to Sharples, four sovereign reverse dies were destroyed in December 1934 (Eigner, https://www.drakesterling.com/news-wire/post/the-1934-melbourne-sovereign), while Mullett states that all sovereign dies in stock at the Melbourne Mint were destroyed in April 1934 (p48, Mullett, Gold Coinage and Refining at the Melbourne Mint, 1992). This apparent conflict is difficult to reconcile as both men had access to the Melbourne Mint's records. Perhaps all sovereign dies in stock were destroyed earlier in April, prior to the arrival of the 1934-dated sovereign reverse dies towards the end of April. If all obverse dies had been destroyed prior to the arrival of the new reverse dies, this would explain why no 1934 Melbourne sovereigns appear to have been struck, even though the Melbourne Mint went to some effort to acquire appropriate dies. This would also explain the destruction of a further four sovereign reverse dies in December 1934 - the exact number and type received at the end of April 1934.
Mullett's records show no 1932 Melbourne sovereigns, 1933 Melbourne sovereigns or 1934 Melbourne sovereigns as having been struck (p48, Mullett, Gold Coinage and Refining at the Melbourne Mint, 1992) and while the records are not completely authoritative, the lack of any such coins seems to prove them right.
Although Australia had become its own country in 1901, an Australian coinage was apparently not the first priority, with concrete action only being taken in 1909.
According to the Royal Mint (IBSCC, Australia Pattern Florin 1909 (Silver) in Counterfeit Report December 1979, No. 263, December 1979):
On the 15th June, 1909, the Colonial Secretary received a cable form the Governor General of Australia asking him to contact the Royal Mint about the preparation of dies for a proposed issue of distinctive Australian florins, shillings, sixpence and threepences. The designs specified in the cable were, for the obverse, the Royal effigy and, for the reverse, a map of Australia with the word, "Australia", superimposed. On the 23rd June the Royal Mint received Treasury approval to prepare the dies and sketch of the proposed reverse designs was sent to the Colonial Office the next day. AS the same time the Royal Mint informed the Colonial Office that it was proposed to use the standard crowned effigy and the inscription, "King and Emperor". On the 8th July the Colonial Secretary received a cable from the Governor General approving the Mint's proposals. By the 6th August, 1909, the florin matrices had been completed reverse punches were almost ready.
It was on the 6th August that a message was received by the Royal Mint from the Representative of the Australian Government in London to suspend the work pending reconsideration of the form of the Royal Style and Titles. Towards the end of September the Australian Government agreed to a proposal by the British Treasury that the inscription should be same as that on the Imperial coinage. At the same time, on the 25th September, the Colonial Secretary received another cable from the Governor General, asking for the substitution of the Australian Coat of Arms for the map. The Royal Mint accordingly prepared new designs, which received the King's approval early in October.
There remain in the Royal Mint Museum a matrix, punch and die for the florin reverse superseded in September 1909, plus an electrotype of florin size, prepared from these tools.
The single known electrotype seems to have remained largely unknown - it was pictured in the September 1964 Australian Coin Review, and rose again to prominence when it was forged by David Gee (whose fake used the wrong obverse design).