Once a manuscript has been submitted to an editor by an agent will an editor make a point to send back a response, whether positive or negative? Or is it customary that the particular manuscript only be brought up again if the editor is interested? Does an agent having to follow-up with an editor inherently bode ill for the project?
Some editors get back to me promptly.
I've sold books to editors I've had to track down with a Snarkscope, duct tape, and Killer Yapp riding shotgun.
There is no industry standarad on this. You can't even say all the editors at one publisher respond the same way.
Every agent I know follows up on submissions. It's just part of the job.