This interests me as well , you often find farthings and halfpennies and pennies very worn from the mid 1850s to 1859 , I know copper is a lot softer than bronze but really I suspect many coins must have been accepted at face value probably until the late 1870's .
I dont think this is an unreasonable thing to the public to do after all these coins had quite a worth of copper in them .
I strongly think this might have happened though it might have only been acceptable in the big citties of the time ,London , Birmingham, etc.