I recently had an event where the party got split. It was easier for to write a private thread to one group, then a separate private thread to not-that group. Easier to remember. Only issue, some of the people in the not group have told me they did not see the sentence aimed at them.

I have since re-written it as to both groups, but it seemed odd that players told me they didn't see a post sent to a not-group that didn't include them.

Is this an issue?

from my past experience with this - make sure everyone is in the correct groups - I personally have screwed that up by Not putting someone in their correct group before. Makes it really hard for them to see the group post.

I kind of thought that creating a not-group would catch everyone you didn't put in it.