The variety is most definitely known to exist, it's just that it isn't acknowledged as "worthy of being published" by most popular texts. Unlike
Morgan dollars, for example,
Trade dollars have languished in the numismatic backwaters for decades.
Certainly, a variety such as this is easily recognized, as easily as some of the doubled dies or overdates in other series, and is certainly scarce. If it were in the
RedBook, or the CP guide, its value would skyrocket. For now, it is of interest to a small group of specialists in the series. That could change, of course.