Charles II Silver Teaspoon

This tea (or coffee?) spoon ticked a few of my collecting boxes: made 300 years before I was born, fully-marked, useful.  The little spoon measures a shade under 3 7/8 inches.  The rattail is very worn on the back of the bowl, and the leading edge of the bowl is slightly curled. 

The teaspoon dates to 1678, and I believe is a bit unusual in that it is fully hallmarked.  In the July/August 2016 issue of The Finial, Granville Gregg poses several questions about English teaspoons, one of which is "When was the first English teaspoon made and by and for whom?"  Eric Delieb, in his Investing in Silver, illustrates a fully-marked Charles II teaspoon bearing the date letter for 1679 (Delieb 18) (which appears to have been most recently sold by Shrubsole). 

Although the maker's mark is not fully visible, it could be IM, a match for which I have not come across in Jackson's, or possibly IK for John King who Jackson identifies as a specialist spoonmaker whose mark is found on spoons between 1667 and 1683 (Jackson 127).

Do any other collectors out there have early fully-hallmarked teaspoons in their collection?

Sources:
Delieb, Eric.  Investing in Silver. New York: Clarkson N. Potter Inc., 1967. Print.
Gregg, Granville. "Musings on Spoon Volumes - Part I." The Finial 26/06 (Jul/Aug 2016). Print. 
Pickford, Ian, ed. Jackson's Silver & Gold Marks of England, Scotland & Ireland. 3rd ed., 1989. Woodbridge: 
       The Antique Collectors' Club, Ltd., 2011. Print.