It would appear, then, that Vance limits his creation of neologisms in other languages to his crime fiction, while he reserves his English ones to other genres.

The nature of the mistake excludes the possibility of a mere typo since the proverbial dangerously small amount of knowledge is so manifestly involved. My money is massively on Vance, as the probability that the original ms would correctly have mentioned a "tokonoma" only to have it changed by an intercepting agency into "takemono" is virtually nil.