On the topic of breaking off the necks and replanting them...
I know that this will work to continue the plant you just harvested. it works much better if there is a few feeder roots coming off the neck which are also left behind.
However, with the shifting of the market toward quality over quantity, and the availability of seed on the market, I would personally discourage this practice.
Here's why. As the market moves toward favoring higher quality and the powers that be have us under a microscope, I think it is best to leave your harvested roots intact. Not only does it show the export inspectors the true age of our harvested plants (better for our long-term ability to continue to harvest ginseng) but it also improves the quality considerably. If you were to bring me a bucket of beautiful ginseng every root large and bulby the size of my thumb...but all the necks were broken off, I guarantee you it would cost you as much or more than a pound of seed would cost. That bucket of ginseng without the tops is now slightly damaged. Some damage is unavoidable and happens. Everyone expects that to a very slight degree. However, if those necks are not in the bottom of the box, the USDA inspectors can refuse export to the shipment of ginseng. Certainly this is an exceptional example, but who wants to take those chances when prices are as high as they are this year?
I really would suggest taking seed with you, and when you decide to harvest a plant, harvest the whole plant. Dig it without damage, wash it lightly, and dry it properly. And please folks....start using those 99 cent plastic shoe boxes from Walmart instead of the plastic bags to carry your ginseng!