In the UG it mentioned that "You cannot add contacts with the same name and at least one other identity field (phone or email) that is the same", as shown below:

The correct error message also shows up when you try to add an existing person with the same name and at least one other identity field, but there is a way to add duplicate people using the method explained below:
Find an existing contact with a different name from the one you want to change to be the same. Say his index in the displayed list is 4. Then, edit his name to the one u want to change to, for example, edit 4 n/Jayden Smith. Now edit his other details seperately one at a time, for example his email, such as edit 4 e/charlotte@example.com. Now you have 2 similar contacts which is not supposed to be allowed. As shown below, there are 3 similar contacts after I have edited their details, at index 4, 5, and 6.

In addition, this also contradicts with what was mentioned in the UG under the Editing a contact: edit section:

In the UG it mentioned that "You cannot add contacts with the same name and at least one other identity field (phone or email) that is the same", as shown below:
The correct error message also shows up when you try to add an existing person with the same name and at least one other identity field, but there is a way to add duplicate people using the method explained below:
Find an existing contact with a different name from the one you want to change to be the same. Say his index in the displayed list is
4. Then,edithis name to the one u want to change to, for example,edit 4 n/Jayden Smith. Nowedithis other details seperately one at a time, for example hisemail, such asedit 4 e/charlotte@example.com. Now you have 2 similar contacts which is not supposed to be allowed. As shown below, there are 3 similar contacts after I have edited their details, at index4,5, and6.In addition, this also contradicts with what was mentioned in the UG under the
Editing a contact: editsection: