Card.cs

public partial class Card : Node2D
{
	private Label labelField;
	private string _label = "";

	[Export]
	public string Label {
		get { return _label; }
		set {
			if (labelField == null) {
				return;
			}
			
			_setLabel(value);
		}
	}

	private void _setLabel(string value) {
		_label = value;
		labelField.Text = _label;
	}

	// Called when the node enters the scene tree for the first time.
	public override void _Ready()
	{
		labelField = GetNode<Label>("%Label");
		_setLabel(_label);
	}
}