Test scenarios to verify:

  | Test                    | Year | VIN                | License Plate | Expected                  |
  |-------------------------|------|--------------------|---------------|---------------------------|
  | 1. Edit bug fix         | Any  | null (existing)    | "TEST-123"    | Should save without error |
  | 2. Modern + VIN only    | 2020 | Valid 17-char      | Empty         | Should work               |
  | 3. Modern + plate only  | 2020 | Empty              | "ABC-123"     | Should work               |
  | 4. Modern + neither     | 2020 | Empty              | Empty         | Should fail validation    |
  | 5. Pre-1981 + neither   | 1970 | Empty              | Empty         | Should work               |
  | 6. Pre-1981 + short VIN | 1965 | "ABC123" (6 chars) | Empty         | Should work               |