Hey, that is a great find! Really beautiful.
I, too, thought 'coin silver' meant silver from melted-down worn-smooth coins. 90% silver content.
And from the Brits I have always heard about 'pounds sterling', with the 'sterling' meaning sterling silver. Sterling silver I also assumed meant pure silver.
But I am no expert even though my ancestors emigrated to the States in the 1870s from Liverpool.