I have created a smart campaign that is going to a very large number of people so I do not want to mess anything up on this. There is a filter in the flow " Lead Source - Not Contains - NSCHBC. When I go to the schedule > Smartlist set to affect "X" number of people, I click that number to test against it. I take a couple leads with that lead source and search them in that schedule list and they do appear. So it's not working and I can't figure out why. There are numerous filters in this flow step, and I do understand filter logic. But this, I can't understand why they are showing in the schedule list when I filter them out like that.
Do you have to use "Not Contains"? Have you tried "Is Not"?
You could try adding those people to a static list and instead use "Member of List - Is Not - [Static List Name]".
If that filter is in the flow as you say, then that is the reason why. Campaign qualification happens at the Smart List level. If your filter is set up as a choice in the Flow then the leads will still qualify for the campaign but wont qualify for that specific choice in the Flow. You may want to consider putting that filter in the Smart List instead.
I would try the positive statement
Lead Source = X
Lead Source CONTAINS X.
then plug in this smart list as Member of Smart List NOT IN to ensure your other campaign excludes these people.
I suspect CONTAINS is not working the way you think.