When an existing member registers, they may already have a member record. If there is a matching email address, the system will simply update the members record. Care should be taken when expecting registrations from family members who share an email address.
On a member registration form, you can decide if new data provided on the registration form, should override existing data on the old member record, or not.
If you must have 2 member records, with the same email address, then the web master can deliberately add the second member record, and bypass the step to edit the existing member record.
A temporary password will be sent to the new member if this has been requested as an option on the registration form. The customers old password will continue to work also, until such time as they change their password. Then only the new password will work.
A password reminder is a bit irrrelevant for member registrations, if you need to first authorise the record to have higher level of access. If they login before having a higher level of access, they may only be able to update their details, and be a bit confused. If you need to have a manual authorisation confirmation process, then please do not auto send a password. Add a message to your form saying that accounts are created within 1 business day, or something like that.
Sometimes there will exist mutliple member records for an email address already. This can happen if a webmaster deliberatly adds new records., either via a form, or via CSV import using unique reference numbers associated with the member record.
Or if a member has 2 accounts, on different email addresses, then changes their email addresses.. There is no automated merge. Webmaster can manually merge the accounts.
How can the member record already exists?
If a person enquires or purchases goods, then they will have a member record. If they have subscribed then they have a member record.
The difference between member records usually comes down to membership groups or membership levels.
A registration form is treated as a subscription, increasing a members level to "opt in" but does not downgrade their level, if they were already an authorised user for example.