object/nightwatch/4 matches the site

public static HumanMadeObject NightWatch_4_Statements()
{
    var nightWatch = new HumanMadeObject()
        .WithContext()
        .WithId("https://linked.art/example/object/nightwatch/4")
        .WithLabel("Night Watch by Rembrandt");

    var materials = new LinguisticObject()
        .WithClassifiedAs(
            Aat.MaterialsStatement,
            Aat.Statement)
        .WithContent("Oil on Canvas")
        .WithLanguage("300388277", "English", "en");
    
    nightWatch.ReferredToBy = [materials];

    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.

var humanMadeObject = new HumanMadeObject
{
    Context = ["https://linked.art/ns/v1/linked-art.json"],
    Id = "https://linked.art/example/object/nightwatch/4",
    Label = "Night Watch by Rembrandt",
    ReferredToBy =
    [
        new LinguisticObject
        {
            Content = "Oil on Canvas",
            Language = [Aat.English],
            ClassifiedAs =
            [
                new Type("http://vocab.getty.edu/aat/300435429", "Material Statement")
                {
                    ClassifiedAs = [Aat.Statement],
                },
            ],
        },
    ],
};

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.