Japanese plant names should not be considered the same as western clonal varieties IMO. Think of them more as "categories" of a type. There are many exceptions, for example V. falcata "Seikai" is always what it is said to be, though there may be look-alikes that are derived from crosses with other forms.
Plants of V. falcata derived from seed cannot be considered "the same" as the parent, even if they "come true" from seed. An example would be seedlings from a Manjushage selfing - they may look like the parent, but they are not the original. The original plant is one of a kind, and can only be reproduced through division (to my knowledge they have not been widely meristemmed, if at all). Since all marginally variegated forms of this species do not come true from seed, they are necessarily all divisions of the original plant, or are impostors. In the case of seedlings from a selfed named plant, they are properly labeled as "seedlings of So-And-So", however to call them So-And-So is misleading, but happens all the time. Reliable dealers will let you know this before you buy them. The original plants are as a rule far more rare, and also generally more expensive.
Mike, I'd "abuse" your plant more during the winter rest if you can - more light, less water, colder conditions, less humidity, NO fertilizer... all may help in getting it to flower. Now it sounds like an over pampered plant, and based on the beautiful plants you grow, I can believe that! Put it outside in the elements and give it a good kick once in a while 
