This rule "No simultaneous submissions" bothers me a lot. It's present in most, if not all submission guidelines. I understand that publisher doesn't want other publishers to have the exact same novel, that is perfectly understanding and valid point. Problem is, at least in my experience, most publishers will not answer to your submission, ever. Not even a short formal letter of rejection which I would really appreciate. There is usually no time limit for answer, and writers are supposed to wait months, if not a year, before they submit their novel to another publisher. Usually, even then you don't get your answer. That is unfair to authors.
Plea to all publishers: if you want to include "No simultaneous submissions" please, at least set the time limit "if you don't hear from us in x weeks/months, consider your work rejected". Or, create rejection template mail and just add our mail to it and send. Because, this way, honestly, as unknown writer who is not a celebrity, I feel like I am at the bottom of a pool. Like, I don't matter, my work doesn't matter, my time and effort doesn't matter. And I am forbidden to try with someone else.