My dad and my nephew have the same first name, "James". My dad's contact has his middle maintained name so I can differentiate between them. When I search for "James" in my contacts only my dad's contact shows up in the search results. When I go to edit that contact it has my nephews birthday, not my dads.

My Yahoo contacts are synced to my android phone. When I look at my contacts on my phone, there is an entry for each of them and they have the correct birthday.

Stop trying to make the Yahoo contact list "smart" the old version was much better. At least it showed the data accurately.