```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, which can contain strings or other nested crates.
    :return: A list of item names extracted from the crate.
    """
    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, which can contain strings or other nested crates.
    :return: The deepest nesting level of the crate.
    """
    if not isinstance(crate, list):
        return 0
    
    max_depth = 0
    for item in crate:
        if isinstance(item, list):
            depth = crate_depth(item)
            if depth > max_depth:
                max_depth = depth
        elif isinstance(item, str) and item:
            # Item names do not contribute to depth
            pass
        else:
            raise ValueError("Invalid entry: expected a non-empty string or a list.")
    return max_depth + 1
```