Geoff,
Furthermore, whether Rev. is speaking of an event and Luke is speaking of several events bears no weight on how the biblical authors decided to translate "apo" as since, unless you wish to furnish an exhaustive linguistic study proving otherwise.
However, several verses translate "apo" as since in regards to the beginning of the world.
Mt 24:21 "For then there will be great tribulation (an event, mind you), such as has not been since the beginning of the world until this time, no, nor ever shall be."
Lk 1:70 "As He spoke by the mouth of His holy prophets, Who have been since the world began.
Acts 3:21 "whom heaven must receive until the times of restoration of all things, which God has spoken by the mouth of all his holy prophets since the world began.
Rom 16:25 "Now to Him who is able to establish you according to my gospel and the preaching of Jesus Christ, according to the revelation of the mystery kept secret since the world began.
Heb 9:26 "He then would have had to suffer often since the foundation of the world; but now, once at the end of the ages, He has appeared to put away sin by the sacrifice of Himself."
So you see, Geoff, that apo is translated as "since" in conjunction with variances of "the beginning of the world" quite often. It appears to me that Rev 13:8 is the abnormality here.
Furthermore, the NASB, NRSV, Holman Christian Standard, Today's English Version, New Century Version, World English Bible, The Bible in Basic English, The Darby Translation, and the Hebrew Names version all prefer to translate 13:8 with "from/since" modifying "names written in the Book of Life" instead of "Lamb slain."
God bless,
Dr. Deutsch
I edited to add the bible translation list.