1872 Die Letter C Farthing
In Spink's 24th September 2019 sale, a reported 1872 die letter C farthing was listed as lot 503 and sold for £1,200. The coin appeared to show a small letter C to the right of the date. The lot description said that the Royal Mint confirmed that the C had not been added post-minting though had no record of die letters being used on farthings.
Die numbers saw much use on silver and gold coins, with die numbers being used on sixpences, shillings, florins, half sovereigns and sovereigns from 1863 until the late 1870s and early 1880s. They saw only limited use on bronze coins however, with a small number of 1862 halfpennies having die letters A, B or C and a small number of 1863 pennies having die numbers 2, 3, 4 or 5. Given that die letters were quickly phased out in favour of die numbers, the use of die letters again a decade later seems unlikely. The use of die markings on farthings almost a decade after their introduction on other denominations is also difficult to explain. It is also reported that die numbers were not used on threepences due to their small size, so their use on farthings would seem further unlikely. It is possible that the letter C is some sort of die damage though this seems unlikely given the apparently perfect shape.
Given that no other examples have come to light yet, either of die letter C or any other die letter, it is difficult to confirm the variety, but such a late discovery is not totally unexpected.