Due to the v4.0 Dueling changes, I noticed that Crescent Moon Style (p. 109) no longer functions in duels as you can no longer keep and spend opportunity during the roll. (Previous changes to the readying weapons rules also limited how it functioned in duels)

can you elaborate abit?

Crescent Moon Style gives you new options to spend Opportunities when performing the Center action.
But, with 4.0, Center no more involves a check (you only roll your skill dice, not making a check) .
No check => no opportunities to spend => can't activate Crescent Moon Style

Still works well enough in Skirmishes when taking the Guard action... but anyway, I never liked how this one played out: no limit on the number of counteratacks while rocking an ungodly TN to be hit, but completely neutered by someone getting into range 0 / shooting you from afar / ignoring you. It's actually a good thing if it gives developers an incentive to rewrite it from scratch !