Almost every big tech IPO of 2019 (Uber, Lyft, Pinterest, Slack, Postmates, Airbnb, Instacart) is headquartered in SF. It's undeniable that the center of silicon valley is slowly shifting north.
The "new" SV is north because all the consumer websites set up shop in SF since all they needed was office and not chip fabs, and they were mostly being worked on by younger folks who wanted to live in the city proper.
Now we have a bifurcated ecosystem where all the hardware folks (and companies) are still in the south bay (and don't kid yourself, there are a ton of hardware startups down here still) and all the consumer stuff is up north.
You just hear about the consumer stuff more because most of the silicon companies are B2B.
I'd really divide it by era. Anything founded before 2005 is in Silicon Valley; after that is in San Francisco. I actually think YCombinator is a big driver of that; they funded younger startup founders (largely Millenials rather than Gen-Xers) who wanted to live in the city.
As a fun side note, the only reason Netflix is in Los Gatos is because the founder wanted it in Santa Cruz, where he lived, but was convinced no one would work there because it would be too far, so he picked the city closest to Santa Cruz that people would still consider Silicon Valley.
What I mean is that it's not the boomers' decision to make in regards to where their money is actually invested.