Talk:Cards/@comment-24904069-20161006120832/@comment-25856498-20161006140952

Consider this scenario.

Prior to the May update, some player has gotten a max stack of level 10 Rare (10 cards extra). Level 11 is then introduced and now the player needs 990 more Rares (the extra Rares collected prior to this became Gold) to upgrade to level 11.

Based on what I've seen, I believe you do have these 300 cards overflow and fill 30% of the upgrade meter if that happens. But that was five months ago, and it might not be relevant anymore.