The last one started going flaky, and would only show up occasionally. Fortunately, I had done a full system backup just the day before the flakiness started. The other two that have failed over time were dead immediately, mostly OS just failing to start one day. But then, most of my many HDD failures were suddenly dead ones
As per the article I quoted, SMART is not that smart. The best regime for storage management is to have reliable system and data backups, which you know how to easily restore from.