It is not stainless in the white. They are not stainless at all, they are regular ordinance grade carbon steel, but "in the white" meaning there is no finish applied after the final polishing by the manufacturer. The steel is left "white". In fact this was a common technique at the time. Even with guns we normally think of as having a dark or brown finish. The brown we now see is really 150 or 250 years of use and patina. Many early longrifles for instance are known to have been in the white because when the barrels are dismounted, the underside, which has been kept from oxidation, is white.
Don't take this wrong, brown, fire blue, and rust blue were also available historically. It is just that white is also a viable historical option, and a very nice one when done right. The true proper final finish for a first grade "in the white" dueling set would be burnished steel.
You got a heck of a deal. Enjoy.
"A Liberal is someone who doesn't care what you do, as long as it's mandatory". - Charles Krauthammer