Please be patient. You will get some answers eventually.
This is not something that has to be fixed right this very second. It can wait.
As to the unofficial change of name, did david ever get married? If yes then does his marriage certificate show an AKA name?
I had a distant cousin who was never adopted by her stepfather but she did use the step fathers surname as hers when she was growing up. When she got married, she had to use her legal name, but she added the notation that she also used an AKA surname as well.