The Q, Z, J, X, K, F, H, (?), W, Y is equivalent to in conversion method 17, 26, 10, 24, 11, 6, 8,?, 23, 25.
The pattern is start with 17, 10, 11, 8 and 23, they're from the conversion but as you can see they have pattern start with ODD, EVEN, ODD, EVEN, & ODD.
However , the remaining numbers are 26, 24, 6, ?, 25, some of them are even numbers but yes they also have a pattern, EVEN, EVEN, EVEN, EVEN (?), ODD. Based of my study, the last number which is 25 is nuisance so let's step it aside in order to understand easily the pattern.
Moreover, the question is what will be the perfect even number to complete my theory? so 26 & 24 have 6 and 4 so maybe we can put on the question mark the number of 4 which is D.
The THEORY is based on what author sees on the pattern including his ideas, perceptions, knowledge and belief.