Hi - I should have asked who was the informant at Marjorie's birth - the person who gave the details to the registrar? Her cert should have signature, description, and residence of informant, who was usually one of the parents.

Having something crossed out on a copy is strange. If a GRO clerk made a transcribing error they could just discard it and pick up another form! Or was it a photocopy of the entry itself?
You could try getting another one from the local RO - say you don't need a certified copy and would like a photocopy of the original entry - it would be worth a try (the entries were copied to send to the GRO, so GRO ones are copies of a copy).

Because adoption was not required to be registered at that time there would be no official papers. Sometimes there would be a private legal arrangement, but these papers were not deposited anywhere and usually show up only as attachments to wills, or are referred to in wills. In England this would apply only to wealthier families. The adoptive parents were often relatives, but if the baby was being advertised (which seems highly unusual) this can't have been the case. If you are in England are you able to check those two newspapers on film, and have a search for the advertisement?

Sue