>>>and others are effectively duplicates e.g. "A" and "a" are the same because Windows file names aren't case sensitive.
>>>A better estimate is 10 digits 0-9 + 26 alphabetic chars, or 36 total chars.
>
>You're right! 60 million it is, then.

Add a few more characters to the base, which are allowed in Windows - parentheses, space, underscore, ampersand, perhaps brackets and braces... it grows.