How do I find the year from a silver date letter?

Identify the assay office mark first, then look the letter up in that office's own table. Match three things, not one: the letter itself, the typeface it is cut in, and the shape of the shield around it. Each office reused the alphabet every twenty-odd years and changed the font and shield each cycle, so the combination gives one year.

Why do two pieces with the same letter have different dates?

Because each assay office ran its own independent cycle until 1975. The letter U in London and the letter U in Sheffield are different years, in different typefaces, in different shields. Using a London table on a Birmingham piece is the most common dating error there is.

Does every piece of British silver have a date letter?

Not any more. The date letter became a voluntary mark in the UK in 1999, so modern pieces may not carry one — although London still applies it as standard unless a customer asks otherwise. Older British silver normally does have one.

Silver date letters, and the shield around them

Almost nothing else in the antiques world will give you a single year. A furniture style gives you thirty. A pottery backstamp gives you a range. A British silver date letter, read properly, gives you one.

It has been doing so since 1478, when a letter was added to identify the warden responsible for that year’s assay, and it changed every year thereafter.

Three things to match, not one

The letter alone is worthless, because there are only twenty-odd of them and centuries to cover. Every assay office cycled through the alphabet again and again, and changed two other things each time round:

The letter.
The typeface it is cut in — roman, italic, black letter, upper or lower case.
The shape of the shield around it — a plain square, a shield with a pointed base, a cartouche with clipped corners.

Together those three narrow to one year. Any one of them alone does not. This is why hallmark tables are printed as pictures rather than as lists: you are matching a shape, not looking up a character.

Find the office first, always

Before 1975 each assay office ran its own cycle, its own fonts and its own shields, independently of the others. From 1975 they adopted a common system.

The consequence is blunt: a date letter cannot be read until you know which office struck it. Reading a Birmingham U off a London table will give you a confident, precise and wrong answer, and nothing about the result will look wrong. This is the most common mistake made with British hallmarks, and it is made by people who are being careful.

So: standard mark, then office mark, then date letter. The assay office marks is how to identify the second one.

When the letter changes

Today the date letter changes on 1 January. Historically it did not — each office changed its letter on its own day in the year, which is why a piece assayed in, say, the spring of a given year can carry the previous letter. For most purposes this does not matter. It matters if you are trying to tie an object to a documented event within a particular year, in which case the change date for that office and that period is worth checking rather than assuming.

Since 1999 it is optional

The date letter became a voluntary part of the UK hallmark in 1999. London still applies it as standard unless a customer asks otherwise, but a modern piece assayed elsewhere may legitimately have three marks and no letter. A missing date letter on an obviously recent object is not a warning sign; a missing one on a piece presented as Georgian is.

What to do with a letter you cannot match

Rake the light across it rather than shining it straight on. Worn punch edges throw shadows and the shield shape usually reappears before the letter does.
Photograph it and enlarge the photograph. A phone at its closest focus, then pinch to zoom, beats squinting.
Check you have not got an import mark. Silver assayed in Britain after 1904 for import carries the office mark in an oval and the standard as a decimal figure. The set reads differently from a domestic one.
Ask the office. For London marks struck before 1975 the Goldsmiths’ Company Library handles historic identification, and the Assay Office handles more recent ones. That is a real service run by the people who keep the registers, and it is the answer when a table will not settle it.