Sync all conversation if they exists

When a conversation is marked as ready, check for previous conversations and sync those too, so we have a completed picture of where things are at.

Start by tracing where a conversation is marked ready and where conversation synchronization currently occurs. Confirm how previous conversations are identified and synced; the work is done when marking a conversation ready also syncs all relevant earlier conversations and produces a complete picture.

Written by the indexing model from the issue text.