Last month, I received the DVD sets volumes 20 and 21. Last night I finally had the chance to sit down and watch a little bit. I was intrigued to see that Joe Caldwell was interviewed twice (as was Paula Laurence--her interview made me regret never having gotten to meet her, particularly since she was a friend of Grayson and Sam Hall's).
It turns out that Joe Caldwell got the gig of writing for DS because he was at Yale and knew Ron Sproat. When Ron started writing for the series, he wasn't always to get his assigned scripts done, so he would turn some of them over to Joe. Eventually Dan learned what was going on and liked Joe's work well enough to invite him to join the staff, which happened around the time of the first Laura Collins story.
Among the best writers for DS so far as I am concerned were Francis Swann (an author of Gothic novels, some of which you can buy cheaply enough on eBay or Amazon vendor), Malcolm Marmorstein, Joe Caldwell, and Violet Welles. Violet also got her start ghost writing for a member of the regular staff--Gordon Russell. I suspect that Violet wrote all of Gordon Russell's final batch of scripts for the series as well, because she mentions going back to the show at the very end and all those shows have Gordon's name on them. I don't know whether Violet was interviewed for any of the DVDs. Violet, according to a print interview that I believe was published by Dale Clark many moons ago, created the character of Count Petofi.
G.
