According to the dialogues & bbb, it's supposed to be, take 3 from me, return 2 deciphered for the first time, and then take 1, return 1 deciphered for the second time. But, I got 3 deciphered cards from 1 on the second time instead. Total of 5. You can see from the screenshot below that I have 2 deciphered cards left in inventory, after I completed the quest.
