Have amended California BC of adopted child, how do we prove it is an amended record?

Just need a little push to get to the end. We have located the (middle aged) person we believe was adopted (the old story was a stillborn child but there is no still birth record, and on phone L.A. County vital records they told me that record was amended... so we had to send to Sacramento to get the amended BC.) What we want to do is acquire some documentary proof that the baby born to our family is the same person who has been assigned the amended birth certificate as their BC. We have the amended BC of adopted child, how do we prove it is an amended record? How can we get the original birth certificate with the same certificate number, or otherwise prove that it is an amended birth certificate and that this person was actually and factually born to our family member? (Please do not suggest asking the family... anyone who knew the truth is since deceased including the birth mother.)