To obtain a Class A operator certificate, you must have held a ham radio license for at least 6 months and have relevant practical experience. This allows you to take the Class B exam and obtain a Class B operator certificate, along with a ham radio license covering frequencies below 30 MHz, after holding it for at least 18 months and having relevant practical experience. To pass the Class C exam, you must also hold a ham radio license below 30 MHz for at least 18 months and have relevant practical experience.
Not passing the C exam will not affect it. If you pass, you need to obtain a license and wait for one and a half years.