One of the biggest possible resources not available in Link+ (California) is the University of California’s libraries. I don’t think any of them are part of Link+.
There’s a borrow button, but when you click on it, it takes you to that library system, and I believe you have to be a member of whatever system you’ve landed on.
I can ask the librarian to order anything in any public library in the US. Items from outside the state take 7 to 10 business days to arrive at my local branch.
It really is mavelous!
This thread makes me wonder if the Union List of Periodicals (ranging from popular magazines to academic journals that I created for the southwestern portion of Virginia back in the early nineties still exists. That was my first professional library job.