I know the problems especially in Ireland.
Several ancestry trees has my b.father dying in the US aged 6 - he never went there as far as I know. His parents names were correct though.
Friend also had an uncle in Ireland but how he came to live with them she never knew or who his blood family was but was accepted as part of the family.
I also have a 1901 census saying someone was the adopted daughter of her aunt but legal adoption didn't start until late 1920's.
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