I have a procedural query question. If my MS is currently out with an editor, following a pitch conference, I understand it is appropriate to note that in my query. Is that information to include in the first paragraph, last paragraph, or even the subject line?
It's a housekeeping measure and you put it in the last paragraph.
And lest you think this is a selling point for your work, let me pour a bucket of cold water on you by telling you it's not.
The reason it's not is that once an editor has read your manuscript, an agent can't go back to him/her with the polished up version you'll have after some developmental work. Your agent in fact can't go to anyone at that imprint again.
There's a reason we BEG you to query agents first and it's exactly for this reason. The editor you meet at the conference may not be the right editor at that publisher for your book. You can't know. We do.
I know it's unbelievably tempting to think of yourself as The Exception to that, but you're not. No one is.
Don't pitch editors at conferences. Talk to them about what they like to read, or what they're specially looking for but if you can hold back on pitching your agent will thank you.