It's a little more complicated than I think you think.
What if a user loads a library and then modifies some of its blocks? Does that count as the blocks coming from the library?
What if I want to use a block that's in two libraries, e.g., LET, and so I load one of the libraries and delete everything except LET. Do both libraries get bolded, or do you want us to remember the actual history of library loading?
What if you loaded an old (e.g., v6) library? Does it still count as having loaded the library?
Yes; bold all the libraries containing the block(s).
All a beginner-reader wants to know (when he/she/__ reads someone else's project with unknown custom blocks) is where the custom blocks can be found. That's all, imho.
The beginner-reader doesn't care about someone else's history.
at the same time, maybe a function to update a block from the current version of the library. If you have a block v6 (from a library) in your project and you want to update this block from the v7 library (to remove javascript code from v6 blocks from a library of our old projects)
I understand what you mean, but I guess it is probably not as easy to implement as my feature request. Can I ask you to create a new topic for your suggestion to make it clear that they're separate feature requests?