CiviCRM Community Forums (archive)

In several databases of about 10K contacts each, I'm seeing zero - 150 contacts that have group subscription dates that pre-date the date_added date (sql example below).  Some affected contacts were from imports, others manually entered.  I have not been able to determine a common thread for them, but my basic question is: how could this happen?
mysql> SELECT MIN(date) as earliest_subscription_date
    ->   FROM civicrm_contact contact_a
    ->   LEFT JOIN civicrm_group_contact ON contact_a.id     = civicrm_group_contact.contact_id
    ->   LEFT JOIN civicrm_group         ON civicrm_group.id = civicrm_group_contact.group_id
    ->   LEFT JOIN civicrm_subscription_history
    ->              ON civicrm_group_contact.contact_id = civicrm_subscription_history.contact_id
    ->             AND civicrm_group_contact.group_id   = civicrm_subscription_history.group_id
    ->  WHERE contact_a.id = 10730
    ->    AND civicrm_group.is_active = 1
    ->    AND civicrm_group_contact.status = 'Added'\G
*************************** 1. row ***************************
earliest_subscription_date: 2011-02-16 12:47:28
1 row in set (0.00 sec)

mysql> SELECT MIN(modified_date) AS date_added FROM civicrm_log
    ->  WHERE entity_id = 10730
    ->    AND entity_table = 'civicrm_contact'\G
*************************** 1. row ***************************
date_added: 2011-03-15 07:55:59
1 row in set (0.00 sec)