If I have the Halloween version of Blake Griffin in my lineup, the "Update Team" button is activated, even though the Halloween version of Blake Griffin has better detailed stats. But the "Update Team" button is greyed out if I have the Elevate version in my lineup.
By free cards, do you mean the Elevate card or Halloween? as I think they were both free. The Elevate version is the only one I can level up and it's at 83.
I still can't understand why the Elevate version shows better stats on the main attribute screen, but worse detailed stats.