I had forgotten all about this:
Apple has discovered that a small percentage of flash storage drives in these MacBook Air models have an issue that may result in data loss. This update tests your drive and, in the majority of cases, installs new firmware to resolve the issue. If your drive cannot be updated, Apple will replace it, free of charge.
This firmware update is recommended for MacBook Air (mid 2012) models.
Eventually, Apple opened a Repair Extension Program for some of these machines.