I don't know very much about the unification timeline in those countries, or about the corresponding articles. I do know that Leti would have described himself as Milanese when in France, Britain, or Amsterdam, and not as Italian. I acknowledge that there is a lot of anachronism on Wikipedia, but have the naieve hope that it can be avoided at least in the articles that I work on and will eventually be fixed elsewhere. I feel like most people on the English Wikipedia know that Milan is in Italy, so we aren't doing them a diservice by being more specific. In short, just because other articles are less precise in their style is no reason to perpetuate that style. Also, I am not entirely sure that the situation is as dire as you describe it in other areas. For example, most residents of Burgundy are refered to as Burgundian rather than French.