That the MARC II standard had been scanned as part of an ERIC project and put online at the Internet Archive. Helpful for me, since I still can't find it at my home or office, even though it's checked out on my account. Luckily, that part is post-pandemic Ruth's problem. My research can continue.
I wouldn't really call it “learned” yet, but I was also working on an OpenRefine tutorial and decided to see what happened when I removed the  in a formula and then realized there might be projects where I wanted to see the data as an array, not just the  instance. Most of the things I'm working on with this formula should be an array of 1 or an empty array … but now I'm thinking about where it might not be.
I also learned that working from home gets much harder when you can't pop out to the coffee shop down the street or do anything social at night. It requires even harder boundaries around work/not work.
And I learned, again, that the Requiem my aunt wrote after my mother's death will still make me cry.