Possibly around 1986 ish when I was playing around with loads for Gamebore , those cases could have been from some batches made that included Pure Gold and we made some for a ground owner from near Ruthin which we called Welsh Gold . Have a look on the cartridge box there should be a code which includes the date.
I know someone who was using these about 6 or 7 years ago. He wouldn't say where he was getting them from but claimed they were loaded for the North American market.