The 1847 sixpence is one of the rarest British sixpences. No examples are recorded as being struck and there are no examples in the Royal Mint collection (p9, Coin Monthly, Jul 1973). Davies mentions 1848-dated sixpences with the last 8 over a 7 (p64, Davies, British Silver Coins Since 1816, 1982), as does Rayner (p160, Rayner, English Silver Coinage Since 1649, 1992) suggesting that 1847-dated dies were prepared.
A single well-worn and graffitied example was brought to light in 1973: the Royal Mint inspected it and found it to be of the correct finess and that the date did not appear to be modified but declined to confirm it as genuine as they had no records of any being struck or any examples to compare it against (p9, Coin Monthly, Jul 1973). The British Museum could also find nothing to suggest it was not genuine but also declined to confirm it as genuine (p160, Rayner, English Silver Coinage Since 1649, 1992). In 1982 Davies still listed in as unconfirmed (p64, Davies, British Silver Coins Since 1816, 1982).
The single known example sold in Dix Noonan Webb's auction on 29th September 2010 as Lot 1773.
The introduction of a new obverse on Australian circulating coinage in 1999 saw small changes to the obverse dies for a number of a denominations part-way through the 1999 mintage. The reasons have not been elicited but it is likely that the changes were to optimise production of coins with the new design.
The 1999 two dollar coin was produced with two different obverse dies - the first and less common variety being with a smaller Queen's head and legend further from the rim and the second, more common variety being with a larger Queen's head and legend closer to the rim. The relative size is the most obvious difference but it is hard to spot without an example to compare to.
Survey by author of 1999 $2 varieties from circulation
Although the small head design is less common it is not rare and may be more common in mint sets. Examples of the small head from circulation tend to be in poor condition too.
Following the introduction of Ian Rank-Broadley's new obverse of Queen Elizabeth II in 1999, the obverses on Australian coins underwent a number of small iterative changes, likely in an attempt to improve die life.
In 2001 the 10c piece was produced with two different obverse dies - on the first the designer's initials (IRB) under the Queen's neck are spaced and do not touch, while on the second more common design the leg of the R elides into the B, though the difference can be a little difficult to detect at times as the ellision is prone to filling.
Survey by author of 2001 10c varieties from circulation
I R B (spaced)
I R_B (joined)
Although the I R B (spaced) design is less common it is not rare and may be more common in mint sets.
In 1887 the Indian princely state of Dhar, like many other princely states, issued a unique coinage, though unlike many other princely states its unique coinage was produced in the same style as India's then uniform coinage (p363, Wiggins, British Commonwealth Coins, 1971). It had previously issued dated copper paisas in 1872 but besides these two issues Dhar never produced any other coinage (p363, Wiggins, British Commonwealth Coins, 1971).
Dhar's 1887 issue of uniform-like coinage consisted of only lower-denomination coins, namely the twelfth anna, the half pice and the quarter anna, all of which were struck at the Calcutta Mint. The mintages of these coins are all unknown (p363, Wiggins, British Commonwealth Coins, 1971).
The reverse of the Australian 5c piece has changed in subtle ways on multiple occasions since its introduction in 1966. The exact reason for most of these changes has never been advertised but it is likely the changes were in pursuit of improved die life.
One such change was first detected on a small number of 5c pieces in 2007 - the position of the echidna had changed slightly, as had the size of the designer's initials (SD) under the echidna. On the older type reverse there was a noticeable gap between the top of the echidna and the rim and the letters SD had curved tops and bottoms; on the newer type reverse the gap between the top of the echidna and the rim was much smaller and the letters SD had flatter tops and bottoms and were also smaller in general.
Examination of 5c pieces dated 2007 and onwards showed that the small SD/low echinda type was being replaced by the new tiny SD/high echinda type: clearly the Royal Australian Mint had a large supply of 5c reverse dies though as the old design has been used up to and including 2016. With the exception of 2007 the new design has been used to produce the majority of 5c pieces, suggesting that the initial change occurred late in 2007.
Survey by author of variety break-downs from circulation
While no small SD/low echinda coins are known in circulation for 2008, 2011, 2013, 2015 or 2016, they are known to exist in various mint-produced sets for those years. Of them, the 2011 seems to be the least common small SD/low echinda year in sets. The 2012 small SD/low echinda is also widely-thought to be a non-circulating coin but it has been detected in circulation in small quantities by the author.
It is likely that the anomalous 2014 small SD/low echinda is the last circulating example as until it appeared the variety's use on circulation coins had been rapidly decreasing and it has not appeared in circulation since.