Jesus Ascension Bible Verse

Is it proven that verses were added to the bible that wern’t original?

Such as Jesus’ ascension into heaven?

There is some evidence that the Ascension in the Gospel of Mark was added after 400 AD, over three centuries after the gospel was written. The Codex Vaticanus and the Codex Sinaiticus, the two earliest versions, written c. 400 AD both end at 16:8, but later versions include an extra twelve verses

John 20 Bible Memory Improvement Scripture Memory Improvement Tips Verses New KJV by AJ Baltes