I take it from the Silverplate Numbers entry that the "10" here would indicate 10 grams used on this 5" fork rather than a total used per a gross bath. Also, can we confirm "Flat Rose" to be an official pattern name?
Flat Rose is the name of the pattern that I've seen used. If it were Sterling (or .830 used commonly with MA) I would expect a 5" 2 prong fork to be around 15 to 20 grams, give or take, so I'd think that 10 grams on one silverplate fork unlikely.