Patti:
I don't pretend to be an expert all things
DS, but Frid was 43 when he started on the series in the Spring of '67.
Moltke? Well, maybe she had a good agent. Actually, Joan Bennett is the "star" of the series and Moltke was what would be called the lead ingenue, I suppose--that could explain it. Or it might because she was so much of the focus in the first year.
Whatever the explanation--without consulting a schedule, I'd say Moltke's last appearance will be sometime in early August...
Actually, despite becoming a documentary filmmaker after her time on the show, Moltke would be much more famous (or infamous) when Claus von Bulow was on trial in the early 80s.
But that, my dear, is a whole 'nother story...
Hope this helps...