You are asked to create a new code to identify students in North Park Secondary School, You are free to use any alphanumeric characters or symbols in your code. The code should be sufficient for at least $20$ years of use.

a$)$ Clearly and succinctly describe the rules and restrictions of your code $($ex$.$ number of characters, restrictions for each character, hidden meanings, etc.$)$

b$)$ Calculate the maximum version of possible student identifier based on your rules in part $($a$).$ Explain why your code is sufficient for at least $20$ years.