I asked change.org for clarification, because today the signatures weren't updated correctly (for the first time!).
For a long time the signature count was on 183 today, then 2 persons must have signed (there was also a new comment to the petition at the same time), because the count was going up to 185, but the list of signatures stayed the same (So person 184 and 185 didn't show up).
I got an answer from change.org: (04. May 11): <The missing counts are the people, who don't want their name to show up on the list. They have unchecked the box that states "Allow my signature to be seen publicly".>
Probably these signers won't show up in the final report or letter to the Congregation, we can only mention them as hidden signers. We have to find out on this matter.
(I totally forgot about thee hidden signers, excuse me).