I have no idea Mccabe. I think they fixed the problem by correcting the gauge face going forward. I don't know if there was a recall or retrofit action.
I'm not even sure it's not something that was discovered later by the aftermarket but, and I'm only going from my weak memory it seemed like a late / early thing and affected both rallye and non-rallye gauges and that Ma was the one figured it out. Can't swear to it.
Here's a kit to replace your gauge faces with the correct and incorrect non-rallye silk screen
Incidentally and I'm sure about this one. In early 68 B bodies there are 4 diff type of speedos for the non rallye standard speedometers. 2 for 150 MPH and 2 for the 120. It was a readability issue.
Early Long 5 mph tics early on and shorter 5 mph tics later on to help the driver differentiate the speed better on 120 speedo
Early 150 speedo's went from 10 to 150 with the zero and later 68 went from 1 to 15 across the face
Here's both styles for the rallye gauges .. note the temp gauges