Thanks for those details!! That's something that I forgot about.
Yes, the evidence points to the Muncie handle. Specifically for late cars, I know of an 06C BB car with a Muncie handle and rare396bronze mentioned the 06A car.
Why did they replace them? Just like any other warranty part - because it had a problem (esp if they were used hard). The reverse lockout assembly was a bad design and the design was changed - I don't recall when that occurred. There is a service bulletin on it, IIRC.