Even when recorded they often give just the adoptive name of the child and new parents, with no information provided about the child before adoption, other than the correct date of birth.
Incidentally, various legal and social requirements surround access to adoption information, most of it hinging on the age of the individual adopted.
It is not always easy to gain access to information even today about natural parents, something that might make your job harder if you are tracing a 'natural' family tree.