Thank you for your answer 
I finally made it ! I’m sure it’s not the most perfect solution, but anyway, I show you the pictures, for you to see:
When an item is destroyed, it does this:
And in the Event BeginPlay:
And besides, when I save the game, IsTakenArray is saved to, and it works great 
So with that, each item doesn’t need to hold a single variable (I just need to set the length of IsTakenArray as long as the number of items presents in the game.)