- The question that was closed is a specific question: what is the solution to the specific problem of finding threads (containing emails) labeled "To-do" which are currently shown in the inbox. The solution to this might involve searching by emails rather than by threads; but we don't know yet since the problem hasn't been solved.
- By contrast, the question that was left open is a general question (which happened to use the same example): is it possible to search by thread in Gmail?
Clearly, these are not exact duplicates. Please can the question which was closed be reopened?