The facts are these. Aleph and B do not include these verses, but the person who made the copy of one of these manuscripts left a space where these verses belong. Obviously, the person who was copying that manuscript believed these verses belonged in the text. Almost all the other witnesses from the early church include Mark 16:9ff. All these other witnesses are as early and as reliable as Aleph and B. So really there are only very few early manuscripts of the NT that do not include these verses. The vast majority of the early witnesses do include them. So if one goes on the basis of the manuscript evidence (and not a biased theory that says two of the manuscripts are better than all the rest), it is clear that these verses are without doubt part of the original text of Mark.

What clinches the matter is another fact. Mark 16:9ff were part of the gospel readings chosen for several of the important festival days of the early church (e.g. Easter and Ascension). It is inconceivable that the early church would have chosen these verses as part of the Scripture to be read in these important festival services if they would have had any doubt that they are part of God's Word.

So we can say with complete certainty that Mark 16:9ff. are part of the Word of God. The manuscript evidence tells us this. And the use of these verses in the early churh on festival days tells us this.

One argument some people try to use to deny these verses is that some words used in these verses are not found anywhere else in Mark. This argument is not valid. What these verses talk about is not talked about anywhere else in Mark so naturally words will be used that are not found elsewhere in Mark. If this argument were valid, then we would have to throw other parts of Mark out also because there are other parts of Mark about which the same thing could be said. We have no right to do this in other parts of Mark. Nor does anywone have the right to cast doubts on Mark 16:9ff. for this reason either.