Is the Law of 1st Mention in hermenuetics based on where it is first mentioned in the Bible or chronologically?

For example: John 1:1 says, "In the beginning was the Word (Logos)..." Even though this is the 4th gospel (Matt, Mark, Luke, John), it identifies the Logos as existing before the creation of the world, before time began. Would it therefore be the first mention, not the first time logos is used in the New Testament; Matt. 5:37 "let your statement...."