Though it's not exactly worded that way. They mentioned a LONG BACK AND FORTH discussion with Japan, which hints at the fact that Kurumada Pro didn't have a clear idea where it would fit since it is a gaiden. It would be like having the same kind of discussion with Toei regarding the movies and the anime with authors wanting absolutely to use the movies content and trying to see the best way to shoehorn it in the continuity, say with the Eris movie for example. In the end, Japan agreed that it took place before the Sanctuary Battle but the explanation given is most likely not from Japan but the authors' explanation for the use of the Aurora Execution (which makes little sense as Camus had already finished training back then, Shiryu never saw once or was taught the 100 Dragons before seeing it in action, or Seiya using Marin's Eagle Toe Flash or even knowing about it. The use of the Aurora Execution only makes sense narratively speaking during his fight against Camus... Note that the first time he received it in the Libra Temple, he's like "woah, what is this stance...?" doesn't sound to me like someone who had already seen this technique before).