FYI, USCIS seems to have changed the way it is reporting processing times here. Until now, the processing times on this page were always a range. The lower bound of this range corresponded to the median and the upper bound corresponded to the 93rd percentile, as explained here. In other words, a range of 17-22 months would have meant that 50% of cases were completed within 17 months after filing, 93% of cases were completed within 22 months after filing, and that, even at 22 months post filing, 7% of cases were still to be processed. The page now appears to show a single number that corresponds to the 80th percentile. For Seattle, as of this morning, the number is 18.5 months, i.e. 80% of cases are completed within 18.5 months post filing (and, by corollary, even at 18.5 months post filing, 20% of cases still remain to be processed).
Separately, I also want to point out that, based on the (admittedly very limited) data points we have on this forum, here and on the tracker:
At least some people are beginning to receive their convocation ~15 months post filing + have their interview ~16-17 months post filing.
The trend in the Seattle office is positive. See columns N and O in the tracker (Days to interview notice and Days to interview respectively), and how (with a few exceptions) those numbers have been coming down over the last few lines that are highlighted in green.