import itertools

def itertooldict(data, keyorder=None):
    """
    An iterator that yields dictionaries representing the Cartesian product
    of values in the input dictionary.

    Args:
        data (dict): A dictionary where keys are labels and values are iterables.
                    `collections.OrderedDict` is preferred for consistent ordering.
        keyorder (list, optional): Specified order of keys for the product and 
                                    resulting dictionaries.

    Yields:
        dict: A dictionary representing one combination of the Cartesian product.
    """
    if not isinstance(data, dict):
        raise TypeError(f"Input must be a dictionary, got {type(data).__name__}")

    if keyorder:
        if set(keyorder) != set(data.keys()):
            raise ValueError("keyorder must contain the same keys as data")
        keys = keyorder
    else:
        keys = list(data.keys())
    
    values = [data[k] for k in keys]
    
    for combo in itertools.product(*values):
        yield dict(zip(keys, combo))
