They don’t contradict any existing parts; if they did, they’d override them. They’re amendments. They amend the constitution. They change it. That’s how the amendment process works.
I see so now you have changed your position from Override to ammend.
Good at least you are getting closer.
Now explain where the 20th Contradicts Article 2.
ANd before you do note the language in Article 2 of the Constitution Section One Paragrpah 8 is very specific wording. Before he enter on the Execution of his Office he shall take the following Oath or Affirmation.
The 20th is worded thusly: The terms of the President and Vice President shall end at noon on the 20th day of January, and the terms of Senators and Representatives at noon on the 3d day of January, of the years in which such terms would have ended if this article had not been ratified; and the terms of their successors shall then begin.
In other words the 20th sets the time limits when the term of office begins and ends. Article two section one paragraph 8, tells the world before he can begin the Execution of the Office of POTUS one must take the oath.
They don't contradict each other.
BTW Obama retook the Oath.
QED