I’ve always played on the naughty side so I do not know if it will work for the nice side.
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added 3 minutes later
I believe the old method will only work if the cards are not maxed to level 15
you still need to purchase them in war store.
as for finding the values I did that when buying war cards.
you have to keep refining them and search the codes
it’s the code that has -negative value x’s 2 in a row.