People have contested whether Mark 16:9-20 should be included in Mark’s Gospel by noting its exclusion by the Codex Vaticanus and the Codex Sinaiticus, which were assembled in the 4th century A.D. However, we have multiple attestations to inclusion in earlier texts. People have fought against one another on inclusion or exclusion for the past couple of centuries. This issue speaks to the many English translations we have and how we came to form them, which are mainly based on either Greek, Latin, or Masoretic interpretations.
In his letter to Bishop Ellicott (who lived between 1819-1905), John William Burgon wrote the following: “Similarly, concerning THE LAST 12 VERSES OF S. MARK, which you brand with suspicion and separate off from the rest of the Gospel, in token that, in your opinion, there is “a breach of continuity” (p. 53), (whatever that may mean,) between verses 8 and 9. Your ground for thus disallowing the last 12 Verses of the second Gospel, is, that B [Vaticanus] and [Aleph – Sinaiticus] omit them:—that a few late MSS. exhibit a wretched alternative for them:—and that Eusebius says they were often away. Now, my method on the contrary is to refer all such questions to ‘the consentient testimony of the most ancient authorities.’ And I invite you to note the result of such an appeal in the present instance. The Verses in question I find are recognized, In the IInd century,—By the Old Latin—and Syriac Verses.:—by Papias;—Justin M.;—Irenæus;—Tertullian. In the IIIrd century,—By the Coptic—and the Sahidic Versions:—by Hippolytus;—by Vincentius at the seventh Council of Carthage;—by the “Acta Pilati;”—and by the “Apostolical Constitutions” in two places. In the IVth century,—By Cureton’s Syr. And the Gothic Verss.:—besides the Syriac Table of Canons;—Eusebius;—Macarius Magnes;—Aphraates;—Didymus;—the Syriac “Acts of the Ap.;”—Epiphanius;—Leontius;—ps.-Ephraem;—Ambrose;—Chrysostom;—Jerome;—Augustine. In the Vth century,—Besides the Armenian Vers.,—by codices A [Alexandrinus] and C [Ephraemi Rescriptus];—by Leo;—Nestorius;—Cyril of Alexandria;—Victor of Antioch;—Patricius;—Marius Mercator. In the VIth and VIIth centuries,—Besides cod. D,—the Georgian and Æthiopic Verss.:—by Hesychius;—Gregentius;—Prosper;—John, abp. of Thessalonica;—and Modestus, bishop of Jerusalem….And now, once more, my lord Bishop,—Pray which of us is it,—you or I,—who seeks for the truth of Scripture ‘in the consentient testimony of the most ancient authorities’? On my side there have been adduced in evidence six witnesses of the IInd century:—six of the IIIrd:—fifteen of the IVth:—nine of the Vth:—eight of the VIth and VIIth,—(44 in all): while you are found to rely on codices B and (as before), supported by a single obiter dictum of Eusebius.”
In other words, we have multiple attestations in ancient times to the longer ending of Mark and only a couple of ancient exclusions. You be the judge.
 Burgon, J.W. (1883). The Revision Revised. The Project Gutenberg Ebook 36722 (2011).