I've been curious for awhile about whether Seattle gets much better salmon sushi than the rest of the country (like: enough that it'd be a reason to seek out Japanese food in Seattle).
And FWIW, Japanese expats I know, not necessarily living in Seattle, seem to confirm that the sushi quality here is exceptional. This is largely a product of geography, being relatively close to both Alaska and Japan.
Anyone trying to tell you they are selling you never frozen sushi is likely lying or violating food code.
See FDA Food Code 2017 3-402.11 Parasite Destruction.