The ascension of Queen Elizabeth II to the throne in 1952 resulted in a number of changes to the designs of British coins in 1953, with the farthing being struck with two different obverse and three different reverse designs.
1953 farthing die types
+ points at bead
+ points between beads
F of FARTHING between denticles, I of FARTHING between denticles
F of FARTHING at denticle, I of FARTHING at denticle
F of FARTHING between denticles, I of FARTHING at denticle
Obverses 1 and 2 and reverses A and B have been well known for decades but reverse B* was only discovered in April 2022.
1953 farthing die combinations
Only in specimen sets; proofs struck
Scarce; proofs struck
Common; proofs struck
Only in VIP proof sets
Matte proofs of 1+A and 2+B were reportedly struck as well, apparently for use in photos (presumably to illustrate the new designs).
Following the Great Depression and a gap in production for all Australian silver denominations, the Melbourne Mint began striking sixpences again in 1934. 1,024,000 1934-dated sixpences were struck by the Melbourne Mint, as well as 50 proofs. The comparatively high mintage of proofs was due to the involvement of New Zealand coin dealer Henry George Williams who requested proofs of all denominations in 1934 (Coinworks, https://coinworks.com.au/melbourne-mint).
Overdates of the 4 over a 3 have also been reported.
In 1871 Ralph Heaton and Sons mint in Birmingham was contracted to strike 10c pieces for Canada and in 1872 it was contracted to strike 10c pieces for Newfoundland. During production of one of these denominations, an incorrect die was used resulting in the pairing of an 1871H Canada reverse die with a Newfoundland H obverse die.
In the early 1870s such a mule would likely have been due to a die mix-up - after all, neither reverse die has an identifying country or province name, and the average Briton would not have been familiar with the designs used on coins in other parts of the world.
The mintage of Canadian 1871H 10c pieces was 1,870,000 and the mintage of 1872H Newfoundland 10c pieces was 40,000: just two mules are known. They were probably struck as part of the Newfoundland mintage as Ralph Heaton and Sons struck Canadian 1872H 10c pieces as well, so the relevant reverse dies would have been at hand in 1872.
On February 26th 2022, photos of a PCGS dual slab purporting to contain an unpainted 2020 Australian Olympic Team Courage $2 struck with a 5c obverse die were posted on a Facebook error coin group. According to the owner the obverse die is actually a standard $2 obverse, but the coin is nevertheless a mule as the expected obverse die has TWO DOLLARS as part of the legend below the Queen's head while the coin in question does not. The partner coin in the dual slab was a regular 2020 Australian Olympic Team Courage $2.
No source was given for the mule, but it was reported that another unslabbed example is also known. A video of a 2020 Australian Olympic Team Courage $2 mule had previously been posted on Facebook in 2021.
While a die mix-up is not impossible, it is somewhat unlikely given the incorrect legend. The reason for the lack of paint will probably remain unknown - while it may have been deliberately removed, it is much more likely that the coin was removed from production prior to the paint application step. How this might have occurred is also unclear as it is unknown what steps, if any, would result in struck coins being removed from production prior to painting - given the volume of coins struck, any of sort of manual inspection is unlikely.