Just been studying this error coin from the Spanish Netherlands I recently bought in a large lot at auction, and seems to be an intriguing error.
The 'host' coin is a nice grade Charles VI (the holy roman Emperor) 1714 Liard from Brabrant, Spanish Netherlands. Then fairly lightly struck over the top, about 40% off centre is the design of an earlier Brabrant Liard coin, in the name of Charles II of Spain - a coin design used between 15 and 24 years earlier. So it looks like an earlier coin die gone out of use has been partially over struck on a newer coin.
Seems like an interesting piece and perhaps unique for the type - a 1714 Brabrant liard is a fairly scarce coin anyway. Has anyone encountered a coin like this before? Would it have any impact on the value?
I'll get pictures up asap in the morning! (about 12 hours)