Sometimes when you create an account segment, the segment results appear to contradict your filters.
Take the results below. There is an account filter to show any accounts that have had logins in the past 30 days. However, notice under the Login (Total Events) column, there are some accounts that are listed with 0 logins.
This is because there is a discrepancy between the filter parameters and the segment view. The filter is pulling information from the last 30 days, however the segment view only is set to pull aggregates from the last 7 days. So these accounts have had logins in the past 30 days, they have just logged in more than 7 days ago. If you would like to change the aggregate time values, try customizing your segment view.