There are 3 ways for a member to show in a scheme
Member signs up themselves
Admin adds member through “Add Member”
Admin enrols member to another scheme via “Scheme Enrolment”
The first two can create the member from scratch (so they didn’t exist, now they do), but can also add a member to a new scheme, utilising the basic fields as the common elements between the schemes (name, email) then adding in the scheme specific fields from the form.
The last option is the most basic, with the admin effectively saying “Copy this member’s basic details over to this scheme”, leaving all the other fields (even required ones) empty.