Collaborators not appearing in Collaborators List

On notes shared by another user with me, the Collaborators List on my end (iOS) does not list that user as a Collaborator, therefore appearing as what one would think to be a note shared with no one that came out of nowhere. Notwithstanding, the note does sync on both ends when either user edits it.

#### Steps to reproduce
1. Have someone share a note with you. In my case, it was someone using the Android app.
2. Search the note in your app and enter it.
3. Open the Collaborators List (ⓘ > Collaborate)

#### What I expected

The email address from the person that shared the note with me should be in that list.

#### What happened instead

The list of Collaborators is empty.

#### Simplenote version

4.6.7

#### iOS version

12.0.1

#### Notes

The behavior is consistent with at least the Mac and Web versions, which also have that Collaborator missing.

The issue was reported to support@simplenoteapp.com, and the answer was that Collaborators not appearing in the Collaborators List is an expected behavior, but I do not see how that could be so.

Start by reproducing the issue through the Collaborators List at ⓘ > Collaborate after an Android user shares a note. Compare the iOS result with the reported Mac and Web behavior, then trace the shared-note collaboration flow. Done means the sharing user’s email appears in the list while edits continue syncing between users.

Written by the indexing model from the issue text.