Now that you're over 18, your challenge is with proving that those custody aspects were in effect back when you were under 18 with a green card.
Can he just file N400 and then tell the IO that he can not prove those custody aspect ?
Or such dialogue can go on
IO: "I have to deny your N-400 applicaiton because you are already a citizen. You shoudl file N 600"
the N400 applicant: "I can not prove custody aspect so I don't think I am a citizen that is why I apply for citizenship"
IO: "Yes, you are a citizen"
the N400 applicant:"No I am not"
IO: "Yes, you are a citizen"
the N400 applicant:"No I am not"
IO: "Yes, you are a citizen"
the N400 applicant:"No I am not"
IO: "OK. Prove to me that your father did not have your custody whne your father was natualized"
the N400 applicant:"I can neither prove he has custory nor can I prove he did not have custoidy"
IO: "If you can not prove your father did not have custory then you are a citizen"
the N400 applicant:"OK"
The applicant withdraw and filed N-600 and then run into teh same IO.
This time the IP insist the pplicant could npt prove the father had the custody of him and advised him to withdraw N400
and file N400.
This goes on forever