This question should be on the UEB Literary forum. However, I’ll quote rule 10.9.3c dealing with words involving shortforms that do not appear on the list at the back of the code book: “Use the shortform for quick if it begins the word and is not followed by a vowel or a y.” Then go to 10.12.12 which says that if punctuation, an indicator or a terminator occurs within a word, follow the basic contraction rules.
Other places to look: the definition of letters sequence, the standing alone rule, and this subject was discussed in a Bulletin article (page 41 of the Fall edition) if you want to look there.