I believe listings are always under a non disclosure agreement. In other words, you won't know until announced and you'll hear it first from the exchange/project itself.
What I suggest is following the twitter of the exchanges that you are interested in, It's probably the fastest way to hear about listings.
Correct, yet this is already a usual stuff or kind of agreement between a project and the exchange itself.It do have somehow some NDA which would really prohibits on leaking out listing information until
it would be confirmed as you said such information would be known on Twitter when it comes to announcement. On some exchange which do have a poll listing you can see on what possible coins would be listed.