There should also be an “area not stated” option in search results. Otherwise enabling a filter may silently hide useful older discussions. Members could choose between all threads, threads with a calculated figure, and threads where the necessary details are missing.
Once you separate completed sales from withdrawals, the usable sample may be too small for a broad Tokyo conclusion. That is still better than treating every vanished listing as a buyer found within 26 days.
I would keep the analysis narrow: use consistent neighbourhood boundaries, then record...