eudc-duplicate-attribute-handling-method

eudc-duplicate-attribute-handling-method is a variable defined in `eudc-vars.el'.
Its value is

((email . duplicate))

Documentation:
A method to handle entries containing duplicate attributes.
This is either an alist (ATTR . METHOD) or a symbol METHOD.
The alist form of the variable associates a method to an individual attribute,
the second form specifies a method applicable to all attributes.
Available methods are:
`list' or nil lets the value of the attribute be a list of values,
`first' keeps the first value and discards the others,
`concat' concatenates the values into a single multiline string,
`duplicate' duplicates the entire entry into as many instances as
different values.

You can customize this variable.