My TBR list is broken down into 3 categories; owned, library & to buy. I have in mind a shortlist of the next few books I intend to read, but this is flexible depending on mood & circumstances (e.g. priorty to bookclub, next in series & books borrowed from a friend or library). I read one book at a time.
The owned TBR shelf contains ~160 books sorted into sections; series, fiction, short stories, non-fiction (sorted by subject e.g. travel, biographies, art).
I have about 300 on my GR TBR list because I want to keep track of the books I want to read. I read about 25 books a year but still intend to get to the others. What do you intend to do after 31 Dec; stop reading completely or start looking for new books to read? If you choose books based on previous recommendations or following an author, that's still a TBR, just less concrete.