Neof. Hanamatoi and Neof. Manjushage
 

Since the 3 spurred variety Hanamatoi is included in the Meikan and therefore would have the 3 spur characteristic in its description, can a buyer assume that the plant being offered as a Hanamatoi indeed will yield 3 spurred blooms and have recourse if it doesn't?

Since N. Manjushage is not included in the Meikan and thus doesn't have an official description, can vendors sell plants labeled Manjushage which don't yield 3 spurs with no recourse by the purchaser if single spurred flowers are produced?

Of course you should expect recourse in both cases. Just because the name is not registered doesn't mean that the collecting public won't mind if you simply use a famous variety name on any plant.

With a famous name like Manjushage, the definition of the variety is essentially locked by overwhelming public consensus as well as copious published information. Because of that, if a vendor were to choose to sell a non-three-spur plant labeled as Manjushage, they're just going to be fighting a losing battle.