Fork, knife set John Gilbert, mistery year letters

[naina1st]

Dear Members,
I used to have no problems with UK silver identification as the information about any kind of marks is widely available. However, this case has put me into a dead end.
Set of 6 pair fork-knife by style and maker mark looks very much like by John Gilbert.
The set of hallmarks on the blade of one fork is typical for Birmingham 1871.
But such a set is the only. Other blades are marked with letters Y and Z in square frame.
It is possible to attribute the year letter Z to 1848 but that date does not match Gilbert's mark registration records.
Meanwhile letter Y in such a frame has no matches in the Birmingham Date letters list for period when Victorian duty mark was in use.
The handles have only four hallmarks: J.G. mark, Victoria head, lion passant and Sheffield city mark. The last three marks are worn out but recognizable

The date letter for Sheffield is absent. Therefore it is not possible to clarify the mystery of Birmingham date letters. I did not find any records about John Gilbert's registration in Sheffield as well.
May be somebody can help me to settle all above contradictions?
Many thanks in advance

[Granmaa]

I might be able to help a bit.

As for the frame or cartouche of the date letters, Assay Offices used more than one punch for each year because different sized and shaped objects require different sized stamps. You would think they would have kept the cartouches the same, but this isn't always the case. Most hallmark identification books do not illustrate this.

Miles

[MCB]

John Gilbert of Electro Works, Ryland Street, Birmingham entered a mark at the Sheffield Assay Office in 1841 in much the same style as the one shown for your items assayed in Birmingham. Inference from the register showing a Birmingham address is that the mark was entered for a Sheffield maker to supply Gilbert with finished and hallmarked goods rather than he having a Sheffield place of manufacture himself.
For information four salt spoons in my collection, all assayed in Birmingham with the date letter "X" for 1872-3, show the usual oval shape. Hopefully other forum members will write to confirm they own items assayed there in the following two years with date letters "Y" and "Z" in a rectangular shape.

Mike

[naina1st]

Dear Members,
Thank you indeed for your contribution.
The information seems to be very useful for the further investigation.
Best Regards