Online event registrations generally are not using the Unsupervised matching rule:
- if "Allow multiple registrations from the same email address" is not enabled, everyone is matched on email address only
- if it is enabled, a single or primary registrant will be matched using the Unsupervised rule, but additional registrants will be matched on the Supervised rule
There's also no provision for what happens if the profile used for event registration doesn't have an email address. If the "Allow multiple registrations from the same email address" is not checked, or even if it is checked and you have the default Unsupervised rule, each registration will be a new contact.
What should happen is that all participants should be matched using the Unsupervised rule so you can pick an appropriate rule for your situation.
Two related issues follow this:
CRM-14540warns an administrator if the combination of settings makes it impossible to match duplicates CRM-14541extends this to allow the administrator to pick a different rule for each event
Original post: "Unsupervised contact duplicate rule ignored when 'Allow multiple registrations from the same email address' is not checked"
Individual rules for "Merge Duplicate Contacts"
Name and Email (reserved) - Unsupervised
Email (reserved) - Supervised
Event registration with "Allow multiple registrations from the same email address" NOT checked
If an unknown contact registers to an event with an e-mail address which is already related to a known crm contact, this known contact will be overwriten and registered to this event. This is because the duplicate rule for unsupervised contact creation is not used in CRM\Event\Form\Registration\Register.php, checkRegistration(). I think this is false behaviour and a security issue. For details see http://forum.civicrm.org/index.php/topic,30964.msg134491.html#msg134491