The date of your basic strategy card isn't of consequence. What is important is that your card is from a credible source where the distinctions between different numbers of decks and sets of rules are taken into account. Then it depends on the specific game you're playing as to which play is correct.
The general rule is to never split 4s, regardless of the dealer's up-card, but there's an important exception. Basic strategy says to always split 4s vs. a 5 or 6 when doubling after splits (DAS) is allowed. Additionally, you should also split 4s vs. a 4 with DAS when playing a single deck. So here's your rule:
Split 4s vs. 4,5,6 with DAS in a single deck. Split 4s vs. 5,6 with DAS in double deck and up. Never split 4s when DAS is not allowed.
Now you simply need to know if doubling after splits is allowed on your game (ask the dealer) to be able to make the proper play.
Remember, basic strategy is not subject to interpretation. In a given situation, there is only one correct basic strategy play, and unless you're counting cards or have other additional information, you should play as basic strategy dictates.
The definitive source for the proper basic strategy for any number of decks and set of rules remains The Theory of Blackjack - The Compleat Card Counter's Gide to the Casino Game of 21, by Peter Griffin, which lays out the proper play from 1 to an infinite deck.
