As a nation state, Italy has emerged only in 1871. Until then the country was politically divided into a large number of independant cities, provinces and islands. The currently available evidences point out to a dominant Etruscan, Greek and Roman cultural influence on today's Italians.
I have a number of records referencing the same person; however, the surname is different. For example, I have Annanicola Saviotti, Annanicola Graziani, and Annanicola Placentini, who are the same person, married to Luigi Mizi.
The following is a short chronology of this family:
You don't say which town this is but given the dates I assume that those birth records prior to 1809 at least are actually baptism records. A mother wasn't always present at the baby's baptism but the priest usually got the information correct. He got the mother's surname wrong on just one occasion. 3 out of 4 ain't bad. Death records are not 100 % reliable as it depends on who is declaring the death. Wives' surnames weren't considered that important. In many early parish records they don't even put the surname of the mother on the baptism record of her child. In 1816 civil records are in force and much more attention is paid to accuracy. Hence you are back to the original baptism record for accuracy. For the 1817 processi you are looking at a document (probably the father's death record) which gives the surname provided at time of father's death. Many 'processi' were parish records. Hope this helps.