Abby states that there are 20,736 possible combinations, but later when David is shown accessing the safe, he is only able to enter four digits (0-9). This would allow for 10^4=10,000 combinations. 20,736 = 12^4, which means that additionally, letters or other symbols would be required (e.g. 0-9, A, B).
At this point the Cytron card would be useless as evidence of election rigging or for blackmail, given how easily the card was hacked to begin with, and given the broken chain of custody.