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Your short-stay Schengen visa (C-Visa) allows you to stay in the Schengen Area based on the 90/180 days rule and will be checked upon entry and exit of the Schengen Area.
Entry could be refused should they determine that you have overstayed.
A National visa (D-Visa) for a specific country (such as Italy) would be needed to stay longer. Under what conditions such a D-Visa is issued is specific to each country.