```python
def unpack_crates(crate: list) -> list:
    """
    Recursively extracts all item names from nested crates and returns them in a flat list.
    
    :param crate: List representing a crate, containing item names or other crates.
    :return: List of item names in the order they appear.
    """
    if not isinstance(crate, list):
        raise ValueError("Invalid entry: expected a list.")
    
    items = []
    for item in crate:
        if isinstance(item, str) and item:
            items.append(item)
        elif isinstance(item, list):
            items.extend(unpack_crates(item))
        else:
            raise ValueError("Invalid entry: expected a non-empty string or a list.")
    return items

def crate_depth(crate: list) -> int:
    """
    Calculates the deepest nesting level of a crate.
    
    :param crate: List representing a crate, containing item names or other crates.
    :return: Integer representing the deepest nesting level.
    """
    if not isinstance(crate, list):
        return 0
    
    max_depth = 1
    for item in crate:
        if isinstance(item, list):
            depth = crate_depth(item)
            if depth > max_depth:
                max_depth = depth
    return max_depth
```