It has always been possible to see the original birth entry/certificate of an adoptee at any Scotland's People centre (not online at home given births only viewable over 100 years and formal adoption only started in 1930). The adopted entry showed on the index as NRH but not viewable at the SP Centre. I only know this as I have two family members who were adopted and marked as such on their original birth entry as per any other RCE entry and, as I know their adopted name, I could see the adopted entry shown as at NRH.