The Greek preposition ἀπό (apo) is used in the New Testament to express many different concepts—so many, in fact, that the BDAG devotes three entire pages of fine print to these various concepts. Furthermore, G. K. Beale, in his commentary on the Book of Revelation in the “New International Greek Testament Commentary” series comments on page 702 that the translation “before” in Rev. 13:8 is a “viable” translation and explains why it is. The translators of the RSV of 1971 were very knowledgeable men who carefully considered each and every word in the Greek New Testament paying very close attention to the context. Indeed, they translated the same preposition as “from” in a similar but different context (Rev. 17:8). I did not have the privilege of discussing these translation choices with them, but I am quite sure that they had very sound reasons for the choices that they made. Moreover, for people with who know less than the first three letters of the Greek and Hebrew alphabets to sit in judgment upon them is an act of audaciousness that could scarcely be more ridiculous.
LOL, the agenda driven mistranslation makes the RSV and ESV laughingstocks. You do not change the text to fit your doctrine, you change your doctrine to fit the text. "Apo" never means before. Take a look at your NRSV!!