Jim, I'm no expert either. I had understood what you were saying and looking for and had a feeling you could be right.

Looking again at the supersearch index, I see it does give the date/time of the post, the thread_ID and what we think is the correct message_ID. It might be possible to match that up with the date/time and thread_ID in the threads title although I'm not sure what you do if 2 date times are equal but I don't think that is unresolvable.

It doesn't sound impossible.

For Each record in threads
    Select matching records in index by date/time and thread_ID
    Assign thread record the message_ID
    Next record.

It needs a bit of refinement but what do you think in principle?