In August 2018 the BNS research blog published an article by the present author which described an unusual Edward I mule penny of the Berwick mint. The coin had a type Ia obverse with a double initial cross, coupled with a type IIa reverse.
A very recent detector find has at last revealed a type Ia with a double initial cross obverse linked with a true Ia reverse. This is the only example known to the author.
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BNS Research Blog 