This story, however, only began to circulate during the Edo period, and is of dubious historical origin.

The story is considered to be of dubious origin due to the following reasons:

While Sylvester is almost certainly what the shop claims him to be, other artifacts are of far more dubious origins.

"All fish that pass through it are of dubious origin."

However, as of 2011, the federal government has not attempted to seize the eight examples considered of dubious origin.

Automobiles seem to be the most costly items of dubious origin.

Rasmussen worked from a manuscript he found in Copenhagen, since lost, and of dubious origins.

The idea that the Constitution should apply to corporations as it applies to humans had its dubious origins in 1886.

The money of dubious origin soon infected many institutions and public and private companies.

Imports of garlic of dubious origin have continued to increase.