Always valid vs not always valid domain model

1.cs

public class Company
{
    public void AssignDelivery(Delivery delivery)
    {
        if (!delivery.IsValid())
            throw new Exception();

        _deliveries.Add(delivery);
    }

    public void PostponeDelivery(Delivery delivery)
    {
        if (_deliveries.Contains(delivery))
        {
            _deliveries.Remove(delivery);
        }
    }
}

2.cs

public class Company
{
    [Required]
    [MaxLength(200)]
    public string Name { get; set; }

    [Phone]
    public string Phone { get; set; }

    public void AssignDelivery(Delivery delivery)
    {
        /* ... */
    }

    public void PostponeDelivery(Delivery delivery)
    {
        /* ... */
    }
}

3.cs

public class CompanyDto
{
    [Required]
    [MaxLength(200)]
    public string Name { get; set; }

    [Phone]
    public string Phone { get; set; }
}

public class Company
{
    public void AssignDelivery(Delivery delivery)
    {
        /* ... */
    }

    public void PostponeDelivery(Delivery delivery)
    {
        /* ... */
    }
}

4.cs

public class Phone : ValueObject<Phone>
{
    private string _phone;

    private Phone(string phone)
    {
        _phone = phone;
    }

    public static Result<Phone> Create(string phone)
    {
        if (string.IsNullOrWhiteSpace(phone))
            return Result.Fail<Phone>(phone);

        return Result.Ok(new Phone(phone));
    }
}