Rule 2.B.a says letters sort before non-letters (after breaking down a string to digit and non-digit parts).
$ cat input6 a% az $ sort -V input6 az a%
The input strings consist entirely of non-digits, and based on the above algorithm have only one part, all non-digits (‘a%’ vs ‘az’).
Each part is then compared lexically, byte-by-byte; ‘a’ compares identically in both strings.
Rule 2.B.a says a letter like ‘z’ sorts before a non-letter like ‘%’ – hence ‘az’ appears first (despite ‘z’ having ASCII value of 122, much larger than ‘%’ with ASCII value 37).