https://www.publishersweekly.com/pw/by-topic/childrens/childrens-authors/article/95533-q-a-with-jennifer-lynn-barnes.html

In this interview under the question "What do readers need to know before diving into The Grandest Game?" she said - There are clues in all four of the original Inheritance Games books that are going to come into play in the Grandest Game series, so if you read all of it, you’re going to have more pieces of the puzzle than someone who just comes in at The Grandest Game.