public class MyClass {
    public List<int> Numbers {get; private set; }

public class MyClass {
    public BindingList<int> Numbers {get; private set; }

public class MyClass {
    public List<int> Numbers {get; private set; }
    
    public MyClass() {
        var rnd = new Random();
        var capacity = 10;
        this.Numbers = new List<int>(capacity);
        for(int i = 0; i < capacity; i++) {
            this.Numbers[i] = rnd.Next(0,100);
        }
    }
}

// .... ve formu
private MyClass asdf = new MyClass();
public Form1() {
    asdf.Numbers.ListChanged += Numbers_ListChanged;
    this.RefreshLabel();
}
void Numbers_ListChanged(object sender, ListChangedEventArgs e) {
    this.RefreshLabel();
}
void RefreshLabel() {
    this.label1.Text = string.Concat(this.asdf.Numbers.ToArray());
}
void button1_Click(object sender, EventArgs e) {
    this.asdf.Numbers.Add(int.Parse(this.textBox1.Text));
}