I just checked the dates of manufacture for the two Componon-S lenses I own. The 50 mm., f/2.8 lens has no back lit aperture scale, no stop down lever, and was manufactured in October 1979. It does have a slider in the barrel that switches the aperture mechanism from click stops to continuously variable, but the detents are very slight and hard to feel. Overall, I don't really like this lens too much. Optically it is excellent, as good as you can get for a lens of this caliber; but the lack of both the back lit aperture scale and positive detents make the lens inconvenient to use. I also have a 50 mm., f/2.8 El-Nikkor which, while lacking a back lit aperture scale, has very positive detents and is easy to stop down to the required setting simply by counting clicks. Optically, it is as good as the Schneider, and I can't see any difference in the prints made with either lens. The 80 mm., f/5.6 has both the back lit aperture scale and the stop down lever, and was manufactured in October 1979. This lens is hands down one of my favorites. It is optically excellent, as one should expect from Schneider, and very easy and convenient to use.
One might assume that the change to the operating mechanism was implemented sometime between 10/78 and 10/79, but that's not a certainty. One could safely assume that the change was planned prior to those dates, and that Schneider was simply using up the existing inventory of lens barrels and iris mechanisms at that point before migrating over to the newer style.