The documents I saw were a decade ago. I'm sure they're out there somewhere, but I wouldn't know where to look.
As I understood it, it was possible to add a device to the III to make it sound a warning tone at every instance of a warning appearing, not just the first one, so that the unit would comply with the new FCC regulations, but TWC decided it was too much to have to worry about a 20-year machine. Therefore, since the III would no longer be in compliance with the FCC regulations, it couldn't be used anymore. The Jr. did get that upgrade, however.
According to what I saw back in 2004, the headends were at liberty to simply dispose of the III units instead of returning them, since TWC had no future use for them, anyway. To be honest, I've heard no reports of a III being used beyond 2004. Unless I missed something at the last minute, and haven't heard otherwise in the decade since, there were to be no exceptions to the rule discontinuing all III units by the end of 2004.