When working directly from a Smart List it makes sense to only include tasks that are either unscheduled or scheduled for today and earlier.
If we have something scheduled for a specific day in the future, we often don't want to have it show up in our lists.
To filter out those future tasks add this line as your advanced filter:
scheduleDate today <= isUnscheduled ||
This will only include tasks that are either unscheduled (in the Master List still) or are scheduled for today or before.
If you also plan tasks for a future week or month and want to leave those out too, use this instead:
scheduleDate today <= isUnscheduled || &inFuture ! &&