The traditional materials as a prompt device
Western tradition assigns a material to each anniversary year: paper for the first, cotton for the second, tin for the tenth, silver for the twenty-fifth, pearl for the thirtieth, ruby for the fortieth, gold for the fiftieth. These are not just card shop trivia, they are a fast way to give the AI a texture to work with. Ask for a paper anniversary song and you might get something light and handwritten-sounding; ask for a gold anniversary and the arrangement can lean toward warmer, richer instrumentation, like a fuller string section or a hint of brass.
The material works best paired with the actual number, since the number is what belongs in the chorus. A prompt for a silver anniversary should still say twenty-five years, not just silver, so the vocal has something concrete to sing. If your year does not match a famous material, cotton for two years or leather for three, skip it and just lead with the number and the milestone details instead.