1. A clerical error in transcription or a genealogical error (e.g. faulty research)
2. Error on the person (e.g., infants were exchanged at birth accidentally or not)
3. A child who is assimilated into a family and adopts the surname of the host family. For instance after the death/disappearance of both parents or after a remarriage of one of them (there is no official adoption). Also, children known by their step father's name.
4. Man took wife's name and/or children given the wife's surname.
5. Born from a couple in which the woman was already pregnant from another man at the moment of her marriage (she could have been a recent widow.
6. Illegitimacy - child given mother's surname or a completely different surname.
7. An adoption (as 3 above)
8. A change of identity for whatever reason, e.g. to escape justice, avoid persecution.
9. A corruption of surname or the adoption of a variant or a completely different surname, either phonetically or semantically, in order to get more easily accepted socially.
10. A Christianization or freeing. It was the case with Indian Panises in New France and with slaves who were often given their previous owner's surname or a completely new name based upon the Saint of the Day or on the surname of the priest who presided over the ceremony.
11. Rape (current, in war times, incest (e.g. step father), Lord's Rights-Law of first night.
12. Infidelity (4-6% in good societies).
13. Sexual orgies (the mother remains uncertain of the father, but could not be charged of infidelity).
14. Artificial insemination. Implantation of fertilized egg.
15. Surname chosen
16. Surname assigned
17. Orphan Trains/Wagon Trains