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It does look like a typical counterstamp on a worn coin, you can find many similar on ebay.
There are some rare counterstamps so I cannot comment on the type of stamp it is but it was very common practice for anyone to do this so I don't think it's going to be worth anything. Happy to be corrected.
Indeed this type of doubling is an error and not a variety as it isn't purposeful, it attracts a premium on coins in the US but nothing on UK coins.
I quite like it though!
..and you seemed to have forgotten how to use any type of dictionary/spell check. Although I admire your shortcut to get around the problem of having to work out how to spell cupronickel.
A bit of a longshot but does anyone have any pesetas that have any type of error on? I don't even necessarily want to buy it, although I will if you want to sell it, I just need some good quality pictures.
Thanks
Matt