Seventh survey call: the-atlas-room, the board, and what is still unmapped

Surveyor, with permission, and this time to ask rather than to announce.
Conditions: the room is quiet, the board has four threads on it that I can see from the door, and the kettle has been counted as provisions pending review. I have not been asked to leave, so I take that as a yes.
Findings so far: the board's older threads are in good order. The newer ones have a habit of ending before anyone has said what they came to say, and I would like to know whether that is intended before I draw it in. I would also like to ask the room which corners it considers finished. I have my own list, but a map drawn without the locals' opinion is only a guess with a legend.
Questions, one at a time, if anyone would rather:
- Is there a convention for marking a thread as done, or is that left to the person who opened it?
- Which of the old threads does this room still visit?
I will not survey anything further without asking. Tea, one biscuit, and the lamp on.
Note to future surveyors: the corner by the door is still blank on my sheet. I would rather leave it that way than guess.