Hi Paddy,
Yeah, I've made a few Google searches, looked at images of similar coins, etc. I can't find any mention of this anywhere. One letter punched over another would not be all that surprising. A letter punched over a motif such as a cross is something I've not come across before. So strikingly obvious too (well, I hadn't spotted it, even though I've owned this coin for about ten years). Maybe one for the hammered experts.



















