I once sent a ms to a big agent and she called me to talk about my book. Although she said she couldn't rep it because she didn't know who would buy it, she did say she felt it would sell and that I should keep working on it and keep sending it out.
We talked for about 15 minutes on the phone and then she asked me to let her know when I sold it so she could celebrate with me. (She was telling me it wasn't ready for her or anyone else. I got that. But she was also telling me that it could be one day and that she loved the premise.)
That was 6 years ago. It sold this year and I did email her to let her know that it had sold and that I was putting her in the acknowledgements because she was so supportive of my work. She was thrilled and life goes on.
I know, it's another take on this whole thing. But this kind of thing happens, you know. We do make some relationships along the way with people who take an interest in our work. And it's those relationships that have kept me going over the years because when a professional tells you that you have what it takes but you need to work just a little bit harder to get your work to a marketable place, well, I listen.I've gotten help from several editors and a couple of agents, none of whom ended up repping/buying this book, and I am very appreciative for the honestly they used in talking to me about my work. They helped me see the truly important things in my books and that helped me learn to develop them.
You know what I'm saying, Miss Snark. I'm sure you've made a friend or two along the way and that there are writers you have helped but ended up not repping.
Like the devotion of Snarklings?
And I'm indeed glad to hear of those successes.
The difference here between the original question and what you are talking about is that the agent ASKED YOU to stay in touch. Of course if someone asks for info, it's ok to send. When it's NOT is when it was just a run of the mill turn down, no matter how nice the letter was. Absent the gist of "please do let me know when this sells so I can celebrate with you"...don't.