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.
Victor......The shifter on my 07c Z28 had "MUNCIE" stamped on the handle. The shifter is long gone now, Hurst replacement back in the late 70's, but I am currently looking for a good original now.
As Kurt mentioned above there was a replacement for the reverse detent and I am including a link showing the exploded view of the shifter and the two detents. http://picasaweb.google.com/111239732860979894494/CamarosNetPhotos#5480485472922550210
Also....if you look at the AIM, M20-A4-Item #3, you can see that there were two different part numbers for the shifter lever control. 3934286 for the low performance engines (Saginaw transmissions)...this should be the shifter lever with no stamping. 3934290 for the high performance engines (Muncie transmissions).....this should be the shifter lever with the "MUNCIE" stamping. At the bottom of the sheet there are no revision entries indicating any changes to the above specifications.
Anyway.....just my take on this.