The data either comes from AD or it comes from Windows Networking Protocol APIs that allow for retrieval of a little bit of data (such as installed OS) from a peer machine even if you don't have valid administrator credentials for the peer machine.
What shows up in the reports depends on which discovery methods you had selected in the inventory wizard. If you don't select AD or Windows Networking Protocol but only use IP Address, for example, you're likely to get absolutely no data about a machine that MAP fails to connect to.
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