If frequent flyer/passport info/contact phone numbers have been entered into the booking it would make it easier to determine whether it is the same traveller or just a co-incidence , similarly , if booked through an agent and 'both' pax are booked through the same agent it makes it easier for the airlines to tell . Back when I was an agent I had occassional problems with father and son travelling on the same flight and having identical names ( I have never understood why some parents are so lacking in imagination - why on earth would "John Smith" choose to call his own son "John" as well - this is where we need a 'smiley' for "Shakes head in bewilderment" for some reason women either have more common sense or are endowed with more imagination as mother/daughter with identical names seems much more rare thankfully )