Also fact that portuguese laws at those times stipulated all children needed to be registered within 1-3 months of birth. There were many stories of parents walking in with kids who had already started walking to register them and picking a date of birth 2 months before.
Speaking of clerical errors. My mother was born on sep 11 but all official documents stated she was born on September 14.
And I thought home affairs in rural South Africa was bad
My surname is German so it's probably not much help, do have an aunt who is married to a Serrão though, but in both my surname, and Serrão the inclusion of the umlaut (in mine) or the tilde seems arbitrary. I heard from someone in the dorms with me at college who had the same surname as me (minus the umlauts) that it was only the eldest son who was entitled to the umlauts on the surname, while the younger sons spelled it without them. Thus, what is classed as two surnames is actually one. Same goes for my aunt's husbands family. Some of them spell Serrão with the tilde, some of them drop it. (Have you ever had a foreign surname with a fancy letter in it mangled in the mouth of an official who can barely speak English, let alone whatever language you've got for a surname? Or the headache of when they tell you that you're not on the system because the computer can't register those letters and so drops them hence Serrão would become 'Serr_o' or 'Serro' etc etc.).
Not sure if this helps. Although i seems more how surnames stop being regarded as separate entities (Serrão vs Serrao) due to a grammatical change and are sort of collapsed into one (Serrao/Serro).