As a bit of an update: we went and chatted with SATS Lost & Found on our way back through Singapore; SATS handle bags for both SQ and LX. We (us and a SATS agent) found the bag in a small pile of bags in the back of the baggage hall in SIN T3 where it presumably spent 14 days. The airline bag tag was gone.

We made the Tile sing its "here I am!" song, which made locating the bag very easy.

Truth be told, it's unclear that SATS would have ever found and returned the bag. We noticed that the frequent-flyer tags on the bag were in my spouse's maiden name. We surmise this stymied the bag match -- and if we had filed the missing bag report in her maiden name, we'd have had the bag returned. I'm guessing they just never looked into the contents and/or other descriptors in WorldTracer, and would not have.