I know it's an old post and I probably shouldn't question someone with the name "W Body Geek" but I can't see why this can't be a 2000 or 2001 as well.
You're right. Do you notice how the outer piece of the taillights are 1990-91 and the internal one is 1987-1989. The funny is I saw the same thing on a 1992-93 Honda Accord the other day using 1990-91 turn signals and 1992-93 main fixtures.