After a retest, I can confirm that since launch, Rest's Flower damage does a maximum of 39%. However, and I don't know if this can be considered a placebo, but during my comparison of launch Res Flower and 1.1.3 Rest Flower damage, 1.1.3 was more consistent compared to 1.0.1. I used Rest the same number of times in each version.
1.1.3 Rest Flower damage: 36-37% (not paused), 39% (when training mode is paused)
1.0.1 Rest Flower damage: 32-33% (paused), 34-35% (not paused), 39% (when paused).
Not sure why the amount of damage varies when, in training mode, the CPU shouldn't have made inputs, especially more inputs that when unpaused (I paused right after landing Rest). It's probably a technical flub and means nothing.