The problem is that they use both lower and upper case letters to mark the assay year. Some letters, particularly when worn, look much the same in upper and lower case, for example c & C, o & O, s & S, v & V, w & W, x & X, z & Z.
You are just unlucky to get one of those.
If they had thought it through they would have skipped certain letters (like they do with car number plates) to avoid confusion.