What were all of the "lower-deck" series? Errand of Vengeance, My Brother's Keeper and The Janus Gate come to mind. Were there any others along those lines?
"Errand of Fury" was the trilogy sequel to "Errand of Vengeance" but, of course, the "lower decks" concept had been abandoned by then. (For the purposes of the character appearance matrix I was compiling at the time, I ended up adding "My Brother's Keeper", which probably helped inspire the concept of a LD ongoing series, and the "Crucible" trilogy, mainly because it had so many LD and TAS characters making cameos!)
"Harm's Way", a LD trilogy by Jerry and Kathy Oltion was seemingly abandoned at proposal stage.