In 2021 I had 2 different reservations in one flight with the same name.

When the check in opened they have sent me an e-mail

'With this communication, we would like to inform you that a possible double booking/charge in your name(s) has been noticed in our system.

Please contact us to confirm your reservation.'I called them and I changed one reservation.
I don't know what would happen if I didn't, but definitely they know there is a double booking.