Anyone familiar with Italian microfilmed civil records will have used these indexes. These are most often found annually at the beginning or end of a register. However, there were also 10-year indexes created which are particularly helpful when searching for multiple offspring of an ancestral couple.
Do you check these indexes when pulling the records of your ancestors? I've used the indexes to clarify a name abbreviated in the text of a document, to verify titles given to family members, and to verify the spelling of surnames. I have even seen children designated as "d'ignoti" or "of unknown parents" in the actual record yet the index gives the name of the child's mother or father.
So, don't overlook this resource. They could be helpful!