object/nightwatch/17 matches the site

public static HumanMadeObject Nightwatch_Permanent_Custody()
{
    var nightWatch = new HumanMadeObject()
        .WithContext()
        .WithId("https://linked.art/example/object/nightwatch/17")
        .WithLabel("Painting")  // assume a mistake in the docs?
        .WithClassifiedAs(Aat.Painting, Aat.TypeOfWork)
        .WithClassifiedAs(Aat.Artwork);


    nightWatch.CurrentOwner = [
        new Group()
            .WithId("https://linked.art/example/group/amsterdam_govt")
            .WithLabel("City of Amsterdam Governing Body")
    ];

    nightWatch.CurrentPermanentCustodian = Ulan.Group("500246547", "Rijksmuseum");

    nightWatch.CurrentCustodian = [
        Ulan.Group("500115988", "Getty Museum")
    ];

    return nightWatch;
}

• Metatype classification The second argument classifies the first, not the object: WithClassifiedAs(Aat.Description, Aat.Statement) says this is a Description, and Description is a kind of Statement. The Plain C# form shows the nesting.
• Terms outside the registry The vocabulary registry holds only the terms linked.art itself publishes, so a dataset's own concepts, places and people are written with Aat.Term, Tgn.Place and Ulan.Person, giving the id and the label.

var humanMadeObject = new HumanMadeObject
{
    Context = ["https://linked.art/ns/v1/linked-art.json"],
    Id = "https://linked.art/example/object/nightwatch/17",
    Label = "Painting",
    ClassifiedAs =
    [
        new Type("http://vocab.getty.edu/aat/300033618", "Painting")
        {
            ClassifiedAs = [Aat.TypeOfWork],
        },
        Aat.Artwork,
    ],
    CurrentOwner =
    [
        new Group
        {
            Id = "https://linked.art/example/group/amsterdam_govt",
            Label = "City of Amsterdam Governing Body",
        },
    ],
    CurrentPermanentCustodian = Ulan.Group("500246547", "Rijksmuseum"),
    CurrentCustodian = [Ulan.Group("500115988", "Getty Museum")],
};

Generated from the object the example builds: every property that is set, as object initialisers, with the vocabulary constants where a term is in the registry. The fluent helpers are a convenience, not a requirement; this form and the one as written produce the same JSON.