I have some question on Free Stars on Friday. As I understand it only Blue Medals that were bought with Gems will be replaced if they generated a Star. That means that if the the Star upgrade failed the Blue medal will not be replaced. Is that correct?

Purchased by Gems means that they were purchased from the Fair, from the Hero's Star screen, or with Discount in the Labyrinth. Stars that were obtained from Chest (in the arena or the Guild chests), Heaven Palace, or with shuffle in the Labyrinth do not qualify. Is that correct?

Based on the above statement I have some Blue Medals that were bought with Gems and some that were not. I have some questions on that too.

How are the medals selected for the upgrade attempt. Will the ones that were bought by Gems be used first, last, in the order they were obtained, or some other way.

Is there any way to tell if the medals you are going to use for a specific attempt qualify or not?

The reason I am asking is that I would like to use the medals that qualify on the attempts that have the higher percentage of succeeding.