First off, I managed to get green smiley faces with the check50 on my initial code for Hail, Caesar! But I wasn't satisfied. The reason was that my code seems to have a corner case that the check50 doesn't catch.
If I input lowercase letters (ASCII 97 - 122), my code will work just fine with any key.
If I input uppercase letters (ASCII 65 - 90), my code will mess up if the key > 6 (or a modulo > 6) with letters near the end of the alphabet.
For instance, my input with a key = 4:
HEY ZARDOZ! LIC DEVHSD!
But an input with a key = 10:
HEY ZARDOZ! ROc dKBNYd!
And I still would get all green smileys on my check50...
I got to a point in my code where, if the key was large enough, my check to wrap-around the encryption would mess up and move from uppercase letters to lowercase letters because I was only checking 'isalpha' on each character. I just thought this was weird and felt like sharing. I hope I have explained this well, I can share code (casear-bad) if there is any interest.
I already went back through my code and fixed this error.