Frequently Asked Questions - Birth Certificate

Birth certificate problems for parents
I applied I-130 for my father to get his GC through Consular processing. I'm a US citizen myself. However I got RFE asking for his birth certificate. I have these queries: The supplemental documents for I-130 for parents as per USCIS application only need US citizen's birth certificate and not the parent's birth certificate. So I don't understand why RFE was issued at this stage? My father was born in the time when the birth certificates were not available. As per the dept of state reciprocity website, it clearly states: "Exceptions: Birth certificates are not available to persons born prior to 1968. " Since it is acknowledged by reciprocity that birth certificates are not available, do I still need to provide NABC (Non-Availability of Birth Certificate)?