Please have a look at the plate with Gorham mark.
There is also the dale letter (looks like I for 1876 - not sure). The mystery is in the presence of letters DGF at 90 degree to the word sterling.
I cherish hopes that somebody knows what do those letters mean?
Thanks for everybody who renders help.
naina1st
Thanks for your posting. You moved me to the right direction.
I saw the article by "The Owl at the Bridge" but missed the part regarding letter system for specials introduced in 1898. I was blinded dating the platter from 1876 with letter "I".
Now I have recovered my sight to notice the letter "I" looks more likely as number "1", and the platter is missing the cover (probably marked with number "2").