A. There is no actual evidences that this text was added at a later time. Many have based their assumption that it was added because Eusebius (c. 260-340) uses the sentence "baptizing in my name." in Demonstratio 3 chapter 6 & 7. As a result many have come to conclude that the text must have been added later. However Eusebius does quote the full formula of Matthew 28:19 in other places (Contra Marcellum I.1.9; I.1.36; Theologia III. 5.22; Caesarea 3 (Socrates, Ecclesiastical History 1.8); Psalms 117.1-4; and Theophania 4.8.)

But upon futher investigation, the actual quote from Eusebius does not refer to baptism but rather to the making of disciples by using a shorten version of Matthew 28:19.

 "With one word and voice He said to His disciples: 'Go, and make disciples of all the nations in My Name, teaching them to observe all things whatsoever I have commanded you,'" {Demonstratio 3 chapter 6}

Again does He the same thing in chapter 7:

"He shewed the virtue of the power in His Name concealed from the crowd when He said to His disciples: 'Go, and make disciples of all nations in my Name.'" {Demonstratio 3}