I 1 -30 for my mum

[Winnifred 0]

I filed I 1-30 for my mum outside the country and my birth certificate was registered late. I had a letter from Uscis requesting for more evidence. Currently I have my baptism cert and health records.The letter also states that in addition to the secondary evidence, I should provide the following evidence regarding the submitted birth document:1, if there were any circumstances that prevented the birth from being contemporaneously registered.2. If the civil authority required corroborative evidence or they independently corroborated the birth prior to issuing the birth document. They need copies of those evidence. I do not really understand the two evidences. Do they require an affidavit from my mum on why my birth was registered late ? Also do they require an affidavit from the civil authority that registered my birth? What other documents are needed to be submitted?