Discrepancy in segment count

I’ve noticed a discrepancy in my segment counts. I have one segment (called subscribers) that shows 6237 Contacts in the segment list. The segment includes contacts with email field not empty, and excludes membership in another segment that I have for unsubscribes/bounces. That segment has 445 contacts according to the segment list.

However if I schedule an email to the subscribers segment it only shows 5807 Pending.

To cross check the subscribers segment I created another segment with the same filters. This segment only shows 5819 contacts.

I’ve given cron plenty of time to run and update the segments. To test I manually added a contact and confirmed that the segment counts increased by 1.

Why would these segment counts be different?

Some contact has not all field… you can check them and delete them.