They don't send rejection letters, so the only way you know that you didn't make it into the book is when other writers start writing or posting on Facebook about the fact that they did.

And it often takes a long time for them to let you know.

I detail more about the submission and rejection/acceptance process here:

https://writingcooperative.com/ive-been-in-10-chicken-soup-collections-if-you-want-to-break-in-here-s-my-advice-9ef3612aacd9?sk=6c27d62414166cd590200f19316115bb

Good luck!