Merging states You 'always' merge profiles into the surname with the lowest ID. If you have 3 profiles, you still merge each profile into the lowest ID. Do NOT do intermediate merging, even if someone is PM on both.
If Chapin-2386 was merged into Chapin-2385, then Chapin-2385 merged into Chapin-1413, and then someone does a search for this person. If they select Chapin-2386 from the Search Results page or directly enter that Wikitree ID, the system will try to bring up Chapin-2386, which will then be redirected and bring up Chapin-2385, which will then be redirected to Chapin-1413.
If you look at the changes log for a 'merged away' profile, the last entry shows a Redirect line to the new profile.