Any Tips on Figuring Out the Last Two Digits of an iCloud Encryption Key?

Hi all, I had the key to decrypt my iCloud account written on the back of a card, but I cut out the image on the card, leaving only 18 of 24 of the encryption characters written down. I have remembered 4 of 6 missing characters, but am missing 2, maybe 3, as seen in the pictures below It was cut out, I got it down to only 2 characters missing left, and Apple Support has refuted any information regarding the key, should I try all 1,296 character combinations to unlock it? I provided a blurred picture of both the card that was cutout, and what I remember on a new card. I think it may be either letter-letter, number-letter, or letter-number, I do not believe it was number-number, which slightly reduces the combination of characters that need to be attempted.