I am taking some taught courses and have decided to create a separate notebook called Courses. I initially put notes on the courses in the Meetings notebook, but for some reason it didn't sit well with me, it felt like those notes didn't belong in Meetings.
I might also get rid off PhD Concepts & Definitions, Ideas & Notes notebook - I have created a document in Scrivener that keeps the definitions important for my PhD, so most of the basic things went there. This notebooks currently contains notes about my ideas linked to organisation of certain project, but I wonder whether those couldn't live in another notebook (e.g. PhD Advice & Resources or Lab Journal). I will see what happens, if it doesn't get much use it will need to go.