Looking back, I have photographic evidence of that sign. Appears to be one more sign along the route as well.
20 BR Williams is something I'd where say "keep in the browser due to lack of clear evidence, but its signed existence hinges on a few signs and we thus need to pay attention unless Caltrans decides to put out a new list." That is, I understand and accept if someone chooses not to clinch it because its existence is not clear, but its removal is not clear enough to definitively say it doesn't exist. Kind of like US 395 BR in Reno, which has enough random signs to qualify as "potentially existing". 20 is the fastest route between me and a lot of the coast, so it's somewhere I expect to be at least every 2-3 years and I can thus check on signs. The other two BRs have been gone for a while.