Since before 1982.
But you reinforce my point, when I said it’s only seen in business names and tourist ads. You quoted the Seattle Convention and Visitors Bureau. It’s not a nickname sincerely used among people who live here.
I used to live in the Seattle area, and I remember when “Emerald City” was chosen, although I had to look up the details of how and when it happened. Nicknames like “Beantown” or “the Big Apple” go back a hundred years or more; and I always got the impression that they sprung up more-or-less organically. “Emerald City” happened within living memory, and was solicited and chosen deliberately.
Yeah, that might not be as comparable, true. It’s more artificial, not something that came about organically.