Because he received a reference from the Medici's (a very powerful family), and already had done some notable work by that time, if I remember correctly. In an

Because he received a reference from the Medici's (a very powerful family), and already had done some notable work by that time, if I remember correctly. In any case upper class Italy was a small world at that time, and personal recommendations, as well as informal sources of information would have been much more important than resumes for conveying past achievements... (but I'm no expert on da Vinci or his time, apart from an essay in my undergraduate years, common sense, and the general gist of a history undergrad...) Anyway, the main point I wanted to make is that the information- flows that are not recorded are often more important, than those that are, especially in historic documents...