Suppose person 'A' is sworn in as Vice President. Then, due to the actions of the 22nd Amendment, for whatever reason they then are sworn in as President. Question: How many yeas may Person 'A' serve in the office of President. ie: The remaining term of the original president, person 'B'. Plus gaining the office in their own right for two more terms?
Two years is the crucial point. Less than two years they get two additional terms if elected. More than two years they may be elected only once.