Alright, did some roadgeeking this morning. And sure enough, my memory and GSV are at least a couple of months outdated, as there's no longer any access across 99 on Royal Brougham between Frontage and Alaskan. Alaskan Way essentially ends/turns into Railroad Way somewhere between Madison and King Streets. The "Ferries" signs on Atlantic west of 1st have been removed, traffic is now directed to turn onto 1st (to Railroad to Alaskan).
Most importantly, I did not see any 519 signs on Atlantic, 1st, or Railroad south of Jackson Street. I didn't look north of Jackson or on 4th Avenue. Dfilpus, if you saw one on Atlantic west of 1st, it's no longer there, but as I said before, you must have been confused. The "North 99" sign visible in GSV is still there.
(I mentioned my memory and GSV being outdated; so is the state highway log, which makes sense as the last (published) data collection was 2012. The log shows 519 taking Atlantic (Edgar) -> 1st (Dave) -> Royal Brougham -> Alaskan. It must be Atlantic -> 1st -> Railroad -> Alaskan now.)