Where this list is silent, the tool says so rather than filling the gap.
25 of the years on this list carry a material. Materials from Debrett's “British Wedding Anniversaries”; royal message rule quoted from GOV.UK.
Why some years come back empty
Debrett's covers each of the first fifteen years, then moves in fives, so plenty of years in between have no British material attached. An empty result isn't a gap in this tool. It's the list.
The strangest of those blanks is the 65th. It carries no material, yet it's a year the palace does write to couples for. The diamond wedding page sets that rule out properly. Two traditions, never squared with each other.
You'll find the blank years filled in elsewhere, borrowed from newer or American lists, and there's nothing wrong with using one. Don't assume a "wax" eighteenth has any British history behind it.
Traditional and modern are two different lists
Where we've confirmed a different modern value, the tool shows it alongside. The clearest case is year thirty: pearl by British tradition, diamond by the newer one. If no modern value appears, we haven't verified one. That isn't the same as the two lists agreeing.
That newer list came out of a jewellers' trade body in the 1930s, which is worth holding in mind when its answer keeps turning out to be jewellery. Where the modern list came from follows the attribution back as far as it goes.
The whole list in one place
If you would rather read every year at once, with the sources and the disagreements set out, see the UK wedding anniversary list.
